Systems for differential ion mobility analysis

ABSTRACT

Disclosed herein are systems, methods and apparatus, for detection and identification of analytes in a volatilized or volatilizable sample, using the mobility-based signature that is produced when the volatilized sample is passed through an ion mobility based analyzer.

REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/305,085, filed on Dec. 16, 2005, now U.S. Pat. No. 7,241,989 which isa continuation of U.S. application Ser. No. 10/797,466, filed on Mar.10, 2004, now U.S. Pat. No. 7,057,168 which is a continuation-in-part ofU.S. application Ser. No. 10/697,708, filed on Oct. 30, 2003, nowabandoned which claims the benefit of Provisional Application No.60/422,534, filed Oct. 31, 2002. The U.S. application Ser. No.10/797,466 is a continuation-in-part of U.S. application Ser. No.10/794,776, filed Mar. 5, 2004, now abandoned which claims the benefitof Provisional Application No. 60/453,448, filed Mar. 10, 2003. The U.S.application Ser. No. 10/797,466 claims the benefit of U.S. ProvisionalApplication No. 60/453,451, filed on Mar. 10, 2003 and U.S. ProvisionalApplication No. 60/530,815, filed on Dec. 18, 2003. The U.S. applicationSer. No. 10/797,466 is a continuation-in-part of U.S. application Ser.No. 10/462,206, filed Jun. 13, 2003, now U.S. Pat. No. 7,005,632 whichis a continuation-in-part of U.S. patent application Ser. No. 10/321,822filed Dec. 16, 2002, now U.S. Pat. No. 6,806,463 a continuation-in-partof U.S. patent application Ser. No. 10/123,030 filed Apr. 12, 2002, nowU.S. Pat. No. 6,690,004 and a continuation-in-part of U.S. patentapplication Ser. No. 10/187,464 filed Jun. 28, 2002, now U.S. Pat. No.7,045,776 and claims the benefit of U.S. Provisional Application No.60/389,400 filed Jun. 15, 2002, claims the benefit of U.S. ProvisionalApplication No. 60/398,616 filed Jul. 25, 2002, and claims the benefitof U.S. Provisional Application No. 60/418,671 filed Oct. 15, 2002. TheU.S. application Ser. No. 10/797,466 claims the benefit of U.S.Provisional Application No. 60/453,287, filed Mar. 10, 2003, claims thebenefit of U.S. Provisional Application No. 60/468,306, filed May 6,2003, and claims the benefit of U.S. Provisional Application No.60/549,004, filed Mar. 1, 2004. The U.S. application Ser. No. 10/797,466is a continuation-in-part of U.S. application Ser. No. 10/321,822, filedDec. 16, 2002, now U.S. Pat. No. 6,806,463 which is acontinuation-in-part of U.S. application Ser. No. 09/358,312, filed Jul.21, 1999 (U.S. Pat. No. 6,495,823).

This application is related to U.S. application Ser. No. 10/187,464,filed Jun. 28, 2002, which is a continuation-in-part of U.S. applicationSer. No. 09/896,536 filed Jun. 30, 2001 entitled “Apparatus ForSimultaneous Identification Of Multiple Chemical Compounds;” and claimsthe benefit of U.S. Provisional Application No. 60/340,894 filed Oct.30, 2001 entitled “Compound Identification By Mobility Dependence OnElectric Field,” U.S. Provisional Application No. 60/334,804, filed Oct.31, 2001 entitled “System For Ion Mobility And Polarity DiscriminationAnd Identification Of Chemical Compounds”; U.S. Provisional ApplicationNo. 60/340,904, filed Dec. 12, 2001 entitled “System For Ion MobilityAnd Polarity Discrimination And Identification Of Chemical Compounds;”U.S. Provisional Application No. 60/342,588 filed Dec. 20, 2001 entitled“Field Dependence Of Mobilities For Gas Phase Protonated Monomers AndProton Bound Dimers Of Ketones By Planar Field AsymmetricWaveform IonMobility Spectrometer (PFAIMS);” and U.S. Provisional Application No.60/351,043 filed Jan. 23, 2002 entitled “Method And Apparatus For FAIMSDetection Of SF6”. The entire teachings of the above disclosures areincorporated herein by reference.

BACKGROUND OF THE INVENTION

Spectrometers are used in chemical analysis for identification ofcompounds in a sample. In some cases a quick indication of presence ofparticular compounds in a sample is needed, while at other times thegoal is complete identification of all compounds in a chemical mixture.Accordingly, samples may be taken directly from the environment andanalyzed or may be prepared by processing and/or separating theconstituents before spectrometric analysis.

Spectrometers based on ion mobility have been used to detect variouschemical and biological compounds. Such spectrometers includeion-mobility spectrometry (IMS) and differential ion mobilityspectrometers (DMS) which are also known as field asymmetric waveformion mobility spectrometers (FAIMS)

Commercially available IMS systems are based on time-of-flight(TOF-IMS), i.e., they measure the time it takes ions to travel from ashutter-gate to a detector through an inert atmosphere (1 to 760 Torr.).The drift time is dependent on the mobility of ions in a low electricfield based on size, mass and charge, and is characteristic of the ionspecies detected. TOF-IMS has been used for detection of many compoundsincluding narcotics, explosives, and chemical warfare agents, and atleast one TOF-IMS system has been adapted for use in a field-portabledevice for detection of bacterial spores in the environment.

DMS devices offer an alternative to the low field TOF-IMS ion mobilityprocess. In DMS, ion filtering is achieved based on accentuatingdifferences in mobility of ionized molecules in a high field. The highfield mobility differences are used for “signature” identification ofchemical species in an ionized sample. DMS filtering is an efficientprocess, combining controlled neutralization of unselected ion specieswhile passing selected ion species for detection.

There is a strong and continuing interest in improved approaches tosample characterization, particularly as may be provided in compact andportable devices.

SUMMARY OF THE INVENTION

Practices of the present invention are directed to methods and devicesfor detection and identification of analytes in samples using themobility-based signature that is produced when a volatilized sample ispassed through a differential ion mobility spectrometry (DMS) device.Any volatized or volatilizable sample can be analyzed including organic,chemical, agricultural or biological samples. In one embodiment, thepresent invention includes using DMS to generate separation data and atleast one other processing step that yields its own separation data.This additional separation step may be before or after DMS filtering.Analytes are reliably identified based on this combination of data.

In one embodiment, the samples subjected to the analysis by the methodsand devices of the present invention are either normally existent in thevolatile state or require volatilization. Analytes in a sample can bevolatilized with or without fragmentation. Analyte volatilization andfragmentation can be achieved by any of the techniques known in the artincluding pyrolysis, thermodesorption, laser ionization, microwaveheating or chemical transformation. Either prior to or following thevolatilization, analytes in a sample can be additionally separated usingany of the techniques known in the art such as gas chromatography.

Each analyte is detected by its ion-mobility based signature. Thissignature is expressed as stored spectrometric data uniquely identifyingthe species being analyzed. The combination and relative abundances ofvarious analytes in a sample forms a pattern that can be used toidentify the entire sample by use of the stored reference data.Preferably the ion-mobility based signature is based on the differentialmobility of that species as experienced in the compensated DMS filterfield.

Analysis of physiological samples can identify diseases, monitorpatient's condition or provide forensic information; analysis ofenvironmental samples can detect chemical or biological contamination,including agents of chemical and biological warfare, or determinegeochemical composition of soil and sediments; analysis of food qualitysamples can detect bacterial and chemical contamination as well as earlysigns of decomposition; analysis of chemical samples can be used tomonitor small and industrial scale processes as well as safetyconditions; analysis of biological samples can be used to identifymicroorganisms in pure or mixed cultures as well as assess efficiency ofmedication or other antibiotic compounds; analysis of industrial samplescan be used to monitor the quality of the material; analysis ofagricultural samples can detect pesticides, herbicides as well asanalyze soil and determine quality of crops.

Accordingly, one embodiment of the invention is directed to a method ofdetection and identification of analytes in a sample by an ion mobilitybased device, comprising (a) obtaining a volatilized sample comprisingmarkers that are detectable by an aspect of ion mobility (preferably byDMS); and (b) directing at least a portion of the volatilized sample toa DMS detection device to obtain a mobility-based signature of at leastone marker, wherein the mobility-based signature correlates with ananalyte in the sample, thereby detecting and identifying at least oneanalyte in the sample.

In another embodiment, the present invention is a method of detectionand identification of analytes in a sample, comprising (a) volatilizingat least a portion of the sample to produce a volatilized sample thatincludes markers detectable by an aspect of ion mobility; and (b)directing at least a portion of the volatilized sample to a DMS device,to obtain a mobility-based signature of at least one marker, wherein themobility-based signature correlates with an analyte in the sample,thereby detecting and identifying at least one analyte in the sample.

In another embodiment, the present invention is a device for analysis ofsamples (e.g., biological, chemical, organic, agricultural) using anaspect of ion mobility, comprising (a) a volatilization part; and (b) adifferential ion mobility spectrometry (DMS) device connected to saidvolatilization part.

In another embodiment, the present invention is directed to a fieldasymmetric ion mobility detection system, comprising an input part andan output part, the input part including a volatilization part; at leasta pair of spaced insulated substrates cooperating to define between theman enclosed flow path for the flow of ions from the input part to theoutput part; at least two electrodes opposite each other and defined inthe flow path, the at least two electrodes including at least one filterelectrode associated with each substrate to form an ion filter section;and an electronics part configured to apply controlling signals to theelectrodes, and the electronics part applying an asymmetric periodicsignal across the filter electrodes for filtering the flow of ions inthe flow path, the filter being compensated to pass desired ion speciesout of the filter section.

In one embodiment, the present invention is a method of detection andidentification of analytes in a sample by an ion mobility-based device,comprising directing a portion of a sample into a first separationdevice thereby obtaining a first profile; directing a portion of asample into a second separation device thereby obtaining a secondprofile, wherein at least one of the first and the second separationdevices is a DMS device; and (c) combining the first and the secondprofiles thereby identifying at least one analyte in a sample.

The instant invention advantageously employs differential mobilityspectrometry in a number of heretofore undisclosed industrial, clinical,diagnostic and environmental applications. The methods and devices ofthe present invention enable rapid detection and identification ofcompounds. Such detection and identification can be made rapidly andwith a high level of confidence. Practices of the invention aresensitive to parts per billion and even parts per trillion levels.Furthermore, unlike the devices of prior art, embodiments of theinvention can simultaneously filter and detect both positive andnegative ions of an ion species. Systems of the invention may be usedalone or in combination with other analytical equipment with increasedlikelihood of accurate identification of chemical compounds, even attrace levels, and even for complex mixtures that heretofore have beendifficult to resolve. As a result, an inexpensive, fast and accuratechemical marker (including biomarker) analysis system which can even beprovided in a compact and field-portable package.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of preferred embodiments of the invention, as illustrated inthe accompanying drawings in which like reference characters refer tothe same parts throughout the different views. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the invention.

FIG. 1 is a schematic flow diagram of an embodiment of the invention.

FIG. 2A is a schematic diagram of a separation system of the invention.

FIG. 2B is a schematic diagram of an analysis system of the presentinvention.

FIG. 2C shows a detection scan according to the invention.

FIG. 3 is a schematic diagram of a separation system of FIG. 2A thatincludes an SPME pre-separator.

FIG. 4A is a schematic diagram of an embodiment of the present inventionwith a cylindrical arrangement of the electrodes of a DMS system.

FIG. 4B shows one embodiment of DMS electrodes where the electrodes arecurved or curvilinear.

FIG. 5 is a schematic of an embodiment of the invention with a pyrolysisfront-end.

FIG. 6 is a schematic diagram of an alternative separation method of thepresent invention.

FIG. 7 shows a mass-spectrometric analysis of pyrolysis products of thespores of B. subtilis.

FIG. 8 shows positive and negative ion spectra for picolinic acid inpractice of the invention.

FIG. 9 shows positive and negative ion spectra for dipicolinic inpractice of the invention.

FIG. 10 shows positive and negative ion spectra for pyridine in practiceof the invention.

FIG. 11A shows the full time-dependent DMS spectrum of pyrolyzed B.subtilis spores as a simulant for B. anthracis.

FIG. 11B shows the individual positive and negative ion spectra at 10seconds after pyrolysis.

FIG. 12 shows spectra with putrescine and cadaverine resolved from oneanother in practice of the invention.

FIG. 13 shows background spectra with no sample present on a SPME fiber.

FIG. 14 shows spectra obtained from subject #1.

FIG. 15 shows spectra obtained from subject #2.

FIGS. 16A-C show spectra generated for markers for bacillus sporepyrolysis in practice of the invention.

FIG. 17 shows positive ion spectra for urine headspace detected inpractice of the invention.

FIG. 18 shows spectra for a DMS embodiment of the invention with a GCfront-end.

FIG. 19 shows spectra for the GC-DMS where the chromatographic runtimehas been decreased leading to co-eluting species and showing that apractice of the invention is able to resolve the co-eluted species.

FIG. 20 shows comparison of prior art FID and a DMS embodiment of theinvention for reproducibility for a homologous alcohol mixture.

FIG. 21 shows the results from py-GC-DMS characterization of positiveions for E. coli (A), M. luteus (B), and B. megaterium (C).

FIG. 22 shows the results from py-GC-DMS characterization of negativeions for E. coli (A), M. luteus (B), and B. megaterium (C).

FIG. 23 the profiles from py-GC-DMS analyses of E. coli, Lipid A andmixtures of Lipid A and E. coli.

FIG. 24 shows the compensation voltage versus retention time for the 50peaks of highest intensity in py-GC DMS analyses of E. coli (greysignals) and M. luteus (black signals) for positive polarity ions.

FIG. 25 shows the compensation voltage versus retention time for the 30peaks of highest intensity in py-GC-DMS analyses of E. coli (greysignals) and M. luteus (black signals) for negative polarity ions.

FIG. 26 shows the effect of separation voltage on py-GC/DMScharacterization of B. megaterium in positive polarity.

FIG. 27 shows the effect of temperature on py-GC/DMS characterization ofB. megaterium in positive polarity.

FIG. 28 shows the Peak area versus number of bacteria for B. megaterium(A), M. luteus (B), and E. coli (C).

FIG. 29 shows overlapping prior art TOF-IMS spectra for m-Xylene andp-Xylene isomers.

FIG. 30 shows resolved DMS spectra for m-Xylene and p-Xylene.

FIG. 31 shows positive ion spectra for different concentrations ofmethyl salycilate.

FIG. 32 shows concentration dependence of the invention to methylsalycilate for both positive and negative ion spectra.

FIG. 33 shows total ion chromatograms from GC-MS analysis of emissionsof organic compounds trapped on SPME fibers by sampling plumes fromcombustion of several materials.

FIG. 34 shows mass spectra from direct characterization of grass, cottonand cigarette smoke using atmospheric pressure chemical ionization massspectrometry.

FIG. 35 shows plots of total intensity of product ions versus retentiontime from GC-DMS characterization of emissions of organic compoundstrapped on SPME fibers in plumes from combustion of cotton, paper andgrass.

FIG. 36 shows plots of total intensity of product ions versus retentiontime from GC-DMS characterization of emissions of organic compoundstrapped on SPME fibers in plumes from combustion of cigarette and engineexhausts. Plots can be compared directly to FIG. 35.

FIG. 37 shows topographic plots from GC-DMS characterization ofemissions of organic compounds trapped on SPME fibers in plumes fromcombustion of cotton and paper.

FIG. 38 shows topographic plots from GC-DMS characterization ofemissions of organic compounds trapped on SPME fibers in plumes fromcombustion of grass and gasoline.

FIG. 39 shows plots of ion chromatograms extracted from analyses byGC-DMS of emissions from combustion of cotton (top frame) and paper(bottom frame). Ion chromatograms were extracted from plots in FIG. 37.

FIG. 40 shows plots of ion chromatograms extracted from analyses byGC-DMS of emissions from combustion of grass (top frame) and from engineexhausts (bottom frame), as extracted from plots in FIG. 38.

FIG. 41 shows resolution of a nerve gas and an interferant simulants atdifferent radio frequency field strengths by a DMS device of the presentinvention.

FIG. 42A and FIG. 42B show DMS spectra of both positive and negative ionpeaks, or modes, for a nerve agent stimulant GA.

FIG. 43 shows the effect of reduced pressure on resolution of variouspeaks by a DMS device of the invention. Resolution increases whenpressure is decreased.

FIG. 44 demonstrates a practice of the invention for a series of warfareagent simulants selectively mixed with 1% headspace of aqueous firefighting foam. As can be seen, good peak resolution can be achieved inpractice of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to methods and devices for detectionand identification of analytes in chemical, biological, agricultural ororganic samples using characteristic mobility-based behavior of thevolatilized sample as it is passed through a differential ion mobilityspectrometry (DMS) device of the invention. This characteristic behavioris also referred to herein as a signature, by means of which ion speciescan be separated, detected and identified in practice of the invention.In preferred practices, this signature is ion-mobility based anddetected in gas-phase DMS.

Preferably each analyte is detected at least by its ion-mobility basedsignature. DMS species identification is done by making a speciesdetection and comparing this data to stored data which uniquely identifya species based upon aspects of ion mobility, i.e., differentialmobility. Briefly, the data may include field conditions (e.g.,wavelength, frequency, intensity, among others), compensation voltage (aDC offset, or variations in the RF signal, such as changes in dutycycle, among others) and also may include flow characteristics (such asflow rate or field gradient, among others) and temperature. DMS producesa signature representing differences in ion mobility between high fieldand low field conditions. In one embodiment, a signature used in themethods of the present invention is the combination of the compensationvoltage and a field strength that results in a known spectral outputassociated with the species being analyzed. In a further practice of theinvention, time of flight ion mobility is used to further characterizeaspects of a detected ion species to further assist speciesidentification.

Principles of Differential Ion Mobility Spectrometry

Differential ion mobility spectrometry is a technique for ionseparation, detection and identification. An asymmetric varying high RFfield is established between filter electrodes over a flow path. Ions inthe flow path are driven by the field transversely and eventually areneutralized as they contact the electrodes. However compensation isapplied to return an ion species of interest to the center of the flowand to pass through the ion filter unneutralized. This process isspecies-dependent.

If ions derived from two compounds respond differently to the appliedhigh strength electric field, the ratio of high to low field mobilitymay be different for each compound. Consequently, the magnitude of thecompensation necessary to counteract the drift of the ions toward eitherplate is also different for each ion species. Thus, when a mixtureincluding several species of ions is being analyzed by DMS, ideally onlyone species of ion is selectively transmitted to the detector for agiven combination of compensation and RF field. The remaining ions inthe sample drift toward the filter electrodes and are neutralized uponcontact.

The present invention may be practiced with various configurations.Preferred embodiments feature compact and field-portable, wide-spectrum,dual mode, DMS systems, such as taught in U.S. application Ser. No.10/123,030, U.S. provisional application No. 60/389,400, as well as thedevice described in U.S. Pat. Nos. 6,495,823 and 6,512,224 and incopending U.S. application Ser. No. 10/187,464, filed Jun. 28, 2002, andU.S. application Ser. No. 10/462,206, filed Jun. 13, 2003. The entireteachings of the above-referenced disclosures are incorporated herein byreference.

Application of the Methods of the Invention

The methods of the present invention can be used to analyze any volatileor volatilizable sample. As used herein, the term “volatile” meansevaporating readily at normal temperatures and pressures. The term“volatilizable” means capable of being converted into gas by use of anyof the volatilization methods known in the art. As used herein, the term“volatilization” refers to a process of conversion of solid or liquid toa gas.

In some embodiments, purification, fractionation and/or separation of asample is desired prior to collection of volatile components orvolatilization of a sample or a part thereof. Samples can be optionallypurified or separated before beginning the DMS analysis by any of thestandard techniques known in the art such as HPLC, turbulent flowchromatography, liquid chromatography, reverse phase chromatography,affinity chromatography, supercritical fluid chromatography, gaschromatography (GC), electrophoresis (including but not limited tocapillary electrophoresis, polyacrylamide gel electrophoresis, agarosegel electrophoresis), solid phase extraction, and liquid phaseextraction, preferably using different solvents (e.g.,chloroform/methanol for lipids, water for polar molecules). Thecapillary of the ion source could be filled with silica beads(derivatized or not) or other material to perform chromatography and/orseparation. Volatile or volatilized components can further be separatedinto fractions by any technique known in the art, for example, gaschromatography (GC), desorption/absorption, effusion, condensation,filtration, ion exchange, or the like.

In one embodiment, the sample contains volatile components. A volatilesample can be collected from the source by collecting headspace or anyother technique known in the art such as filtration, distillation,sublimation, vacuum distillation, etc.

Volatile or volatilized components can be directly subjected to DMSanalysis or further separated using any of the techniques as describedherein. In one embodiment, the volatile components are filtered througha membrane to reduce moisture content and other impurities that mayaffect signal-to-noise ratio. One skilled in the art can determine thematerial of a membrane based on the properties of the analytes to beseparated (for example, polarity). Membrane materials can include, forexample, polymers such as Teflon or dimethyl silicon.

In other embodiments, samples do not contain volatile components or maycontain a combination of volatile and nonvolatile components. Whereanalysis of non-volatile components of a sample is desired, thesesamples can be subjected to gas-phase DMS analysis as long as they arevolatilizable. For example, samples of body tissues, pathogens, buildingmaterials or samples of soil may not be volatile, but are volatilizable.Likewise, breath can contain both volatile components and non-volatilebut volatilizable components. These components can be separated asdescribed herein and the volatilizable components subjected tovolatilization and analysis by DMS.

The whole sample or any fraction thereof can be subjected tovolatilization. Volatilization can be performed in the presence orabsence of an oxygen environment. In one embodiment, volatilizationproduces a complex mixture of chemicals referred to herein as “markers”.Markers can include whole molecules or fragments thereof. Thecomposition and relative abundance of the markers in a volatilizedsample uniquely identifies the sample. Such sample may be organic orinorganic, chemical, biological or otherwise.

Any of the techniques known in the art can be used for volatilization.Preferably, sufficient energy is applied to a sample to break intra- orinter-molecular chemical bonds of the analytes in the sample.Non-limiting examples include pyrolysis, thermal desorption, includingtemperature-programmed desorption and thermally assisted solid phasemicro-extraction (SPME), laser ionization, including matrix assistedlaser desorption ionization (MALDI), microwave excitation (heating withmicrowaves), and chemical transformation (e.g., hydrolysis, photolysis,oxidation, etc.).

A particularly useful method of volatilization is pyrolysis. The termpyrolysis (PY) refers to a procedure in which a material is heated,usually in the absence of oxygen, thereby causing the material to breakdown into simpler compounds. Pyrolysis provides a volatilizationtechnique for various types of sample analysis, especially for samplesthat are not easily volatilized. Pyrolyzing a sample produces a complexmixture of volatile, semi-volatile and non-volatile organic chemicals(herein referred to as pyrolysate). Vapors generated during pyrolysiscan be swept directly into a detection device. The composition andrelative abundance of various components in the pyrolysate is a uniquecharacteristic of a given sample. Accordingly, the sample can becharacterized by analyzing pyrolysis products using DMS to produce a“fingerprint,” i.e., signature, that can uniquely identify the sample.

Another method for volatilization of a sample is thermal desorption,which is a widely used technique for extracting and isolating volatileand semi-volatile compounds from various matrices. For thermaldesorption, samples, usually solids, are heated and analytes arevolatilized. Typically, a carrier gas or vacuum system transports thevolatilized components to a detection device. Based on the operatingtemperature of the desorber, thermal desorption processes can becategorized into two groups: high temperature thermal desorption (HTTD)(320 to 560° C. or 600 to 1000° F.) and low temperature thermaldesorption (LTTD) (90 to 320° C. or 200 to 600° F.). It is the techniqueof choice for air monitoring (indoor, outdoor, workplace, automobileinterior, breath, etc.) and is a tool for the analysis of soil,polymers, packaging materials, foods, flavors, cosmetics, tobacco,building materials, pharmaceuticals, and consumer products. Almost anysample containing volatile organic compounds can be analyzed using somevariation of this technique.

Temperature programmed desorption (TPD) is a variation of thermaldesorption whereby the temperature of a desorber is increased in apre-programmed manner to maximize the temporal resolution of theanalytes and contaminants (noise) in a sample. TPD is oftenadvantageously coupled to solid phase micro-extraction (SPME). SPME is atechnique of pre-concentration of analytes whereby the analytes ofinterest are extracted from a sample by absorption into solid phasematerial, usually fibers. Absorption of the analytes by the fibers isbased on the affinity and solubility of the analytes in the solid phasematerial of the fibers. Solid phase materials can include variouspolymers, for example, polyacrylate, polydimethylsiloxane,divinylbenzene and mixtures thereof. Analytes can be extracted fromeither gas or liquid phases. Alternatively, a solid sample can besubjected to thermal desorption and the volatile analytes releasedduring this process can be absorbed by SPME fibers, thuspre-concentrating the analytes of interest. Following the extraction,the compounds are thermally desorbed by a pre-programmed temperatureramping and directed for analysis and detection. An example of asuitable TPD/SPME device is disclosed in Basile, F., InstrumentationSci. Tech. 31(2): 155-164 (2003), the entire teachings of which areherein incorporated by reference.

MALDI is a method that allows for vaporization and ionization ofnon-volatile samples from a solid-state phase directly into the gasphase at atmospheric pressure or in vacuum. Briefly, the techniqueinvolves mixing the analyte of interest with a large molar excess of amatrix compound, usually a weak organic acid. This mixture is placed ona vacuum probe and inserted into a detection device for laser desorptionanalysis. During laser desorption, the matrix that also contains theanalytes is irradiated with lasers in order to transfer the content intothe gas phase. The matrix strongly adsorbs the laser light at awavelength at which the analyte is only weakly absorbing. As a result,the matrix reduces intermolecular contacts beyond analyte-matrixinteractions thereby reducing the desorption energy. The results arehigh ion yields of the intact analyte and giving rise to sub-picomolesensitivity. Principles of MALDI are well-known in the art. MALDIdevices suitable for use with the present invention are described, forexample, in U.S. Pat. Nos. 6,414,306 and 6,175,112, the entire teachingsof which are herein incorporated by reference.

The whole sample or any analyte in a sample can be subjected tovolatilization. In one embodiment, the markers produced byvolatilization of a sample are separated using any of the standardseparation techniques used in the art, for example, gas chromatography.Following chromatographic separation, any or all fractions can besubjected to DMS-based detection.

Various illustrative applications of the methods of the presentinvention are described in detail below under separate headings.Generally, samples can be derived from any source and can includephysiological, environmental, biological, chemical, agricultural andindustrial sources.

Physiological samples such as breath or tissue samples or physiologicalfluids (including blood, urine, synovial fluid, saliva, etc.) can beused to diagnose and monitor patient conditions, including point of carepatient monitoring, and provide forensic information.

Environmental samples such as air, soil, sediments, petroleum, naturalgas or water can be used to detect chemical or biological contamination,including that by heavy metals, and in monitoring of remediation sites,berms, incinerator wastes and water treatment facilities. Methods of thepresent invention can be used for detecting agents of chemical andbiological warfare in a sample.

Food quality samples, such as foodstuff, air samples from refrigeratorsor containers, and swabs of food-contacting surfaces, can be used todetect bacterial and chemical contamination of as well as early signs ofdecomposition during shipping, in monitoring shelf life and/or packagetampering.

Chemical samples, such as samples of reaction mixtures, can be used tomonitor small and industrial scale processes, including the extent ofreactions and detection and separation of stereoisomers, as well as tomonitor safety conditions.

Biological samples, such as samples of pathogens, can be used toidentify microorganisms in pure or mixed cultures as well as assessefficiency of medication or other antibiotic compounds. Industrialsamples, such as samples of medicaments, sample of cosmetic products,samples of building materials, samples of crop plants, fabric, syntheticpolymers and organic materials, can be used to monitor the quality andintegrity of the material.

In one embodiment, the sample includes whole microorganisms,non-microbiotic pathogens or other biological materials. In oneembodiment of the invention, a sample can include protozoan, fungal,bacterial or viral infectious agents, antibodies and other proteins,nucleic acids, peptides, peptidomemetics, peptide-nucleic acids,oligonucleotides, aptamers, lipids, polysaccharides, liposaccharides,lipoproteins, glycoproteins, and small molecules. In preferredembodiments, the sample contains infectious agents and microorganismssuch as protozoa, fungi, bacteria and virus.

The practice of the method of the present invention includes subjectingvolatile or volatilized markers and/or other sample components to DMSanalysis, which can optionally be combined with ion mobilityspectrometry (IMS). IMS is well known in the art.

In alternative embodiments, IMS can be used prior to, following or inparallel with the DMS analysis. The use of IMS can aid and/or supplementDMS analysis in some cases. For example, an IMS device can be used as anion filter to additionally separate and filter the analytes of thesample or the volatilized markers and/or analytes, thus raisingsensitivity and signal-to-noise ratio of the DMS device and itsdetectors. Further, a given sample can be subjected to an IMS analysisin parallel with a DMS analysis. In this embodiment, IMS spectra can becompared to those obtained by a DMS device. By comparing the two typesof spectra, additional information useful in analysis and identificationof the markers and analytes can be obtained.

In a further embodiment, the present invention is a method of sampleidentification, wherein a sample is analyzed and the analytes containedtherein identified by a multi-stage process that includes differentialmobility analysis. In one embodiment, a first stage of sample processingcan include filtering a sample by particle size, a second stage caninclude volatilization and the next stage can include differential ionmobility. In another embodiment, the present invention is a method ofanalysis of complex mixtures that includes coupled Ion Mobility/MultipleStage Mass Spectrometry.

Illustrative Embodiments of Clinical, Industrial, Research and PublicHealth Applications

The present invention can be used in the identification ofmicroorganisms, in clinical, research, industrial, and public healthapplications, including terrorism.

For example, the invention is useful in diagnosing bacterial, viral,fungal and protozoan diseases and infections affecting particularpatients. Patients can be human, primates, companion animals (dogs,cats, birds, fish etc.), livestock (cows, sheep, fish, fowl and poultry,etc.). In a preferred embodiment, the present invention can be used forpathogen identification in mixed cultures, without the need forisolating and culturing of the microorganisms. Briefly, a sample ofinfected tissue, a physiological fluid from a patient or a sample of apathogen culture is volatilized. The pathogen culture can be mixed,i.e., contain more than one type of microorganisms. The volatilizedsample, optionally separated by a suitable separation technique known inthe art, such as gas chromatography, is directed to a DMS detectiondevice of the present invention. Because the volatilized samplecomprises markers unique to the pathogens in the sample, the pathogensare identified. In an alternative embodiment, volatile compounds emittedby the organisms (methane, ammonia, ethylene, plant alkaloids as well asoxygen, carbon dioxide, products of amino acid decarboxylation, proteinand lipids decomposition) can be detected to assess cell growth anddeath as well as other physiological changes.

In one embodiment, the methods of the present invention are used in therapid identification of antibiotic resistant strains of organisms suchas Staphylococcus aureus and Mycobacterium tuberculosis, and mayoptionally be used to determine to which antibiotics or combinations ofantibiotics the particular strain of bacterium infecting the patient issusceptible. Additionally, the invention is useful in distinguishingbetween diseases with similar clinical manifestations but differentcausative agents, with possible differences in the preferred course oftreatment.

In another embodiment, the invention can be used in the identificationof pathogenic and non-pathogenic fungi, as well as determining whichagents are effective against fungal infections. Both the systemicdisease caused by primary pathogens such as Histoplasma capsulatum andthe opportunistic mycoses caused by Candida albicans or Cryptococcusneoformans can be detected using methods of the present invention.Assessment of the type of infectious agent can lead to better methodsfor treatment.

The invention is useful in the diagnosis of at least some of theprotozoan parasites, and especially those, such as N. fowleri, whichrequire culturing for definitive diagnosis. The invention is also usefulin the determination of appropriate treatment of an infection by anyparasite. For example, in some geographic areas, Plasmodium falciparum,the organism associated with the majority of the one to two milliondeaths annually from malaria, has developed resistance to chloroquine,the first-line agent used in treatment. As described herein withreference to bacteria, by detecting relative abundances of the pathogensin a time series of samples, the invention can be used to determine towhich agents the parasites infecting an individual show susceptibility.

In another embodiment, the present invention can be used in thediagnosis of viral diseases, as well as the determination of agents towhich particular viruses show susceptibility. Exemplary viruses whichcan be identified using the DMS analysis of the present invention,either by sampling patient tissues or bodily fluids or after replicationin culture include: Herpesviruses, which infect vertebrates, includinghumans (Varicella-Zoster (chickenpox, shingles), Epstein-Barr andCytomegalovirus (infectious mononucleosis), Herpes Simplex (herpes,Kaposi's sarcoma); Baculoviruses, which infect invertebrates (especiallyinsects such as silk worms); iridovirus, which causes African swinefever; Poxviruses, which infect invertebrates and vertebrates, includinghumans causing Variola (smallpox), Vaccinia, Monkeypox, Mousepox;adenovirus, which infect vertebrates, including humans and causes colds;caulimoviruses, which infect plants; papillomavirus, which causes wartsand other tumors; bacteriophages; hepadnavirus, which infectvertebrates, including humans (Hepatitis B); reoviruses, which infectinvertebrates, plants, and vertebrates, including humans; flaviviruses,which infect vertebrates, including humans causing yellow fever; Denguefever and hepatitis C; togaviruses, which infect plants and vertebratescausing rubella, St. Louis, Eastern/Western (equine) encephalitis;picornaviruses, which infect vertebrates, including humans causingpolio, colds and hepatitis A; potyviruses, which infect plants; variousoncornaviruses, which infect vertebrates, including humans, causingcancer (Avian Leucosis Virus; Murine Leukemia Virus; Rous Sarcoma Virus;human T-cell Leukemia Virus (HTLV); Lentiviruses, which infectvertebrates, including humans, causing HIV (AIDS) and felineimmunodeficiency; orthomyxoviridae, which infect vertebrates, includinghumans, causing influenza; filoviridae, which infect vertebrates,including humans causing Ebola fever, Marburg fever; paramyxoviruses,which infect vertebrates, including humans (Morbilivirus (measles),parainfluinza virus, Rubulavirus (mumps), Respiratory Syncytial Virus(colds, croup); rhabdoviridae, which infect invertebrates, plants, orvertebrates, including humans (Rabies, Vesicular Stomatitis);arenaviruses, which infect vertebrates, including humans (LymphocyticChorioMeningitis); bunyaviruses, which infect plants and vertebrates,including humans (La Cross Virus (encephalitis), Sin Nombre Virus(hantavirus pulmonary syndrome), other hemorrhagic fevers).

The methods of present invention can further be used in determinationand diagnosis of animal and human disease such as Creutzfeld-Jacobdisease, scrapie and mad cow disease, where the infectious agent is aconformer of a wild-type analog.

The present invention can be used for public health monitoring. Thepresence of coliforms, such as E. coli, in waters off beaches is oftenused as a marker for the presence of untreated sewage. The invention canbe used in testing of water samples to determine whether coliforms arepresent, without first having to isolate and culture the variousmicroorganisms in the sample. Volatilization of a mixed bacterial sampleproduces markers unique for each microorganism in a sample. In anotherexample, the invention can be used to determine the presence ofCryptosporidium or Vibrio cholerae in water supplies. The invention canbe used for testing of municipal water supplies and other waters for thepresence of these and other pathogens.

The invention can further be used in the determination of which chemicalagents are effective against the particular organism or strain oforganism infecting a particular patient. Briefly, a time series ofsamples of infected tissue, a physiological fluid or samples of a mixedpathogen culture from a patient being administered a specific chemicalagent are analyzed using aspects of ion mobility as described herein.The methods of the present invention can identify which of the pathogensresponds to the selected treatment. Thus, the invention can be employedin screening novel chemical compositions as antibiotics for theirpotential efficacy as agents to kill or inhibit the growth ofmicroorganisms. In general, screening typically involves dividingcultures of the organism into multiple aliquots. The agents being testedare then introduced into a first group of the aliquots, while a secondaliquot is reserved as a control to which no agent is added. Therelative amounts of the organisms in the first test group are thencompared to the amounts of the organisms grown in the presence of theagents in the second, control group so that the relative effectivenessof the agents being tested can be determined. Large numbers of aliquotscan be cultured and tested in parallel, permitting the testing of largenumbers of potential agents to be tested at once. Due to highsensitivity of the methods of the invention, this embodiment can beparticularly beneficial where large scale culturing of microorganisms isto be avoided.

The general format of microorganism assays employed by the methods ofthe present invention will now be described. For ease of description,the methods described below will be directed toward bacteria, althoughfungi, protozoa and viruses can be employed with modifications familiarto persons of skill in the art.

A specimen to be subjected to analysis, for example blood, urine, mouthor vaginal swab, personal odor, or a sample of food or of water believedto contain a pathogen (e.g. virus, bacteria, fungi or protozoa) isobtained. If not already in the form of an aqueous suspension, thespecimen is usually suspended in an aqueous medium prior to beingsubjected to the process of this invention. The size of the sample isnot critical, provided a sufficient number of microorganisms areobtained to permit the intended procedures to be performed. Further, thenumbers of bacteria present in the aqueous suspension are not critical,provided a sufficient number of bacteria are present for the procedureof this invention to detect differences between test and controlsamples. The time required to perform the analysis, however, can bereduced as the concentration of microorganisms increases.

If the specimen has too low a cell concentration, it may be concentratedby known techniques, such as centrifugation or by culturing. Thespecimen is cultured by incubating under conditions suitable forsustaining bacterial growth. The period of incubation is that periodsufficient to obtain detectable growth, which will differ depending uponfactors such as bacterial species and concentration of organisms in thesample.

After the optional incubation of the test and control specimens for aperiod of time, the specimens are volatilized and quantitatively andqualitatively analyzed using ion mobility detection devices of thepresent invention.

One skilled in the art will readily determine the necessary culturingconditions. The choice of a particular method of culturing themicroorganism or microorganisms of interest is determined by a personskilled in the art.

Analysis of Physiological Fluids and Other Biological Samples

Analysis of physiological fluids and other biological samples by themethods of the present invention can be done by employing any of thevolatilization procedures described herein. In one embodiment, thevolatile components of a sample are analyzed by collecting the volatileanalytes at a headspace of a liquid or solid sample. In anotherembodiment, a liquid or solid sample can be volatilized as describedherein.

Samples can be obtained from a variety of sources. As will beappreciated by those in the art, the sources comprise any number ofthings, including, but not limited to, cells (including both primarycells and cultured cell lines), tissues and bodily fluids (including,but not limited to, blood, urine, serum, lymph, bile, cerebrospinalfluid, interstitial fluid, aqueous or vitreous humor, colostrum, sputum,amniotic fluid, saliva, anal and vaginal secretions, perspiration andsemen, a transudate, an exudate (e.g., fluid obtained from an abscess orany other site of infection or inflammation) or fluid obtained from ajoint (e.g., a normal joint or a joint affected by disease such asrheumatoid arthritis, osteoarthritis, gout or septic arthritis) ofvirtually any organism. Samples can be obtained, for example, fromplants (e.g., crops), invertebrates (e.g., silk worms), non-mammalianvertebrates (e.g., poultry, fish, exotic birds, fowl), non-human mammals(e.g., livestock, companion animals, primates) and humans. Samples canalso be collected from extracellullar fluids, extracellular supernatantsfrom cell cultures, inclusion bodies in bacteria, cellular compartments,cellular periplasm, mitochondria compartment, etc.

In a preferred embodiment, the preparation of samples for the DMS-basedanalysis can be achieved by any method known to those of skill in theart. Sample preparation can include a desalting step to increase thesensitivity and resolution. In addition, as will be appreciated by thosein the art, the combination of preparative steps, solvents, purificationand separation schemes, will all depend on the class(es) of moleculesexpected to be detected.

Samples can be prepared in a variety of ways. One skilled in the artwill readily determine the manner of sample preparation, which depends,generally on the source and the type of analytes expected to bedetected. For example, physiological fluid samples can be prepared by aprotein precipitation followed by a desalting treatment. A solution ofmethanol and water (49:49:2 water:methanol:acetic acid v:v:v) is addedto each of the samples and the samples are chilled. This precipitatesthe proteins to the bottom of the tube. Each tube is then centrifugedand the supernatant decanted. For the desalting step, small amount(approximately 100 mg) of DOWEX ion exchange resin is added to each vialand allowed to sit for approximately 10 minutes. The sample is thencentrifuged and the supernatant removed. This solution is thenintroduced to the an ion-mobility detection device.

Any solvent known to those of skill in the art can be used inconjunction with an ion source in the practice of the present invention.Examples of suitable solvents are dimethylsulfoxide, acetonitrile,N,N-dimethyl formamide, propylene carbonate, methylene chloride,nitromethane, nitrobenzene, hexane, methanol and water. The solvent cancomprise more than one solvent. In a preferred embodiment, the solventis a solution of methanol and water (49:49:2, water:methanol:acetic acidv:v:v). Selection of a suitable solvent will depend on the type ofmolecules is expected to be detected. For example, a solution ofmethanol and water is used as a solvent when the detection of solublemolecules is to be achieved by the ion-mobility device, while hexane canbe used when the detection of apolar molecules such as lipids is to beachieved. In one embodiment of the invention, the sample source (e.g.,tissues, cells) is extracted in different solvents and each extractionsubjected to analysis, so that a more complete analysis of the moleculespresent in the sample source can be accomplished.

Samples can optionally be purified, fractionated and/or separated usingany of the standard technique known in the art as described herein.

In addition, it should be noted that purification and separationtechniques may be simultaneously or sequentially run on samples, indifferent orders and in different combinations. Thus for example, asimple protein precipitation may be run on a portion of the sample, andthen a HPLC step. Similarly, portions of samples (e.g., portions of thecellular populations) may be subjected to different techniques in theelucidation or identification of peaks.

While one skilled in the art will appreciate that the method of thepresent invention can be practiced on a sample obtained from any of thesources mentioned above, application of ion-mobility analysis todetection and identification of urine constituents will now be describedin details.

Urinalysis

An embodiment of the present invention provides a method of urinalysisusing aspects of DMS ion mobility of the urine constituents.

Urinalysis is an examination of the urine by physical or chemical means.Urinalysis comprises a battery of chemical and microscopic tests thathelp to screen for urinary tract infections, renal disease, and diseasesof other organs that result in abnormal metabolites appearing in theurine.

The following is a non-limiting list of indicators present in urine canbe detected: bilirubin (a degradation product of hemoglobin); glucose;hemoglobin (an indication of hemolysis); urine ketones (a by-product offat metabolism and present in starvation and diabetes); nitrite (anindication of urinary tract infection); urine pH (the acidity oralkalinity of the urine); urine protein; urobilinogen (a degradationproduct of bilirubin). In addition, pathogens such as fungi (yeasts),protozoa, bacteria and virus can be detected.

The results of the analyses are used for diagnosing the patients.Specifically, in some situations, an alkaline urine is good. Kidneystones are less likely to form and some antibiotics are more effectivein the alkaline urine. There may be times when the acidic urine may helpprevent some kinds of kidney stones and may prevent growth of certaintypes of bacteria. When blood levels of glucose are very high, some ofthe glucose may show up in the urine. The glucose and the ketones testsare usually done together. Large amounts of ketones may be present inuncontrolled diabetes. Finding protein in the urine is probably the besttest for screening for kidney disease, although there may be a number ofcauses for an increased protein level in the urine. Bilirubin in theurine is a sign of a liver or bile duct disease. Urobilinogen is foundin small traces in the urine. Nitrites and white blood cells are anindication that a urinary tract infection is present. Any vitamin C thatthe body does not need is excreted in the urine. If there are measurableamounts of Vitamin C in the urine, it may interfere with the other urinetests.

Volatile components of a urine sample are colected by directing aheadspace to a DMS detection device. In another embodiment, urine sampleis subjected to gas-chromatographic separation prior to DMS analysis. Inan exemplary procedure, a gas chromatograph is maintained at an initialtemperature designated as T₀. At the onset of analysis, designated astime t₀, the sample is introduced to the inlet of the gas chromatographcolumn. The temperature of the gas chromatograph is then elevated orramped at a constant rate to a temperature T_(r), reached at time t_(r)at which all analytes have completed elution from the column. The columnis further heated to a final temperature T_(f), slightly elevated aboveT_(r), at time t₁, and is held at this temperature to clean out thecolumn. At the end of this final period, designated as time t₂, thechromatograph is cooled back down to the initial temperature T₀ forsubsequent analysis, which cooling down is completed at a time t₃.

In addition to the above, every person emits a particular chemical odor,which may be used as a signature. This odor signature can be detected byDMS practices of the invention. The odor signature can be used toidentify an individual for security applications, to identify bodies,and for covert applications to determine if a terrorist has beenresiding in a particular location based on signatures from urine orother residual odors left at the location. Such signature detection,based on detection of volatile chemicals, may be practiced according tothe present invention.

Breath Analysis

An embodiment of the present invention provides a method of breathanalysis. The present invention provides a method and apparatus that canmeasure and analyze both volatile and relatively non-volatile componentsreleased. Alcohols, such as ethanol, can be detected in exhaled air.Furthermore, understanding the composition of breath analysis can beused to diagnose diseases and elucidate pharmacokinetic properties ofvarious compounds.

Alveolar breath is a distinctive gas whose chemical composition differsmarkedly from inspired air. Volatile organic compounds (VOCs) are eithersubtracted from inspired air (by degradation and/or excretion in thebody) or added to alveolar breath as products of metabolism. Normalhuman breath contained several hundred different VOCs in lowconcentrations. More than a thousand different VOCs have been observedin low concentrations in normal human breath. (Phillips M: Method forthe collection and assay of volatile organic compounds in breath,Analytical Biochemistry 1997; 247:272-278, the relevant parts of whichare incorporated herein by reference).

Alkanes in breath are markers of oxygen free radical (OFR) activity invivo. OFR's degrade biological membranes by lipid peroxidation,converting polyunsaturated fatty acids to alkanes which are excretedthrough the lungs as volatile organic compounds (VOCs); (Kneepkens C. M.F., et al., The hydrocarbon breath test in the study of lipidperoxidation; principles and practice, Clin. Invest. Med. 1992;15(2):163-186).

For example, increased pentane in the breath has been reported as amarker of oxidative stress in several diseases including breast cancer(Hietanen E., et al., Diet and oxidative stress in breast, colon andprostate cancer patients: a case control study, European Journal ofClinical Nutrition 1994; 48:575-586), heart transplant rejection(Sobotka P. A., et al., Breath pentane is a marker of acute cardiacallograft rejection. J. Heart Lung Transplant 1994; 13:224-9), acutemyocardial infarction (Weitz Z. W., et al., High breath pentaneconcentrations during acute myocardial infarction. Lancet 1991;337:933-35), schizophrenia (Kovaleva E. S, et al., Lipid peroxidationprocesses in patients with schizophrenia. Zh Nevropatol Psikiatr 1989:89(5): 108-10), rheumatoid arthritis (Humad S., et al., Breath pentaneexcretion as a marker of disease activity in rheumatoid arthritis, FreeRad Res Comms 198; 5(2):101-106) and bronchial asthma (Olopade C. O., etal., Exhaled pentane levels in acute asthma, Chest 1997; 111(4):862-5).Analysis of breath alkanes could potentially provide a new andnon-invasive method for early detection of some of these disorders(Phillips M: Breath tests in medicine, Scientific American 1992;267(1):74-79).

Breast cancer can be detected by identifying metabolic products of thecytochrome P450-mediated pathways. The cytochrome P450 (CYP) systemcomprises a group of mixed function oxidase enzymes which metabolizedrugs and other xenobiotics. This system also metabolizes alkanes toalcohols e.g. n-hexane to 2- and 3-hexanol. The cytochrome P450 systemis reportedly expressed in cancers of breast as well as other tissues(Murray G. I., et al., Tumor-specific expression of cytochrome P450CYP1B1. Cancer Res 1997; 57(14):3026-31). Recent studies suggest thatexhaled pentane can be used as an additional marker for breast cancer.Hietanen et al studied 20 women with histologically proven breast cancerand a group of age and sex-matched controls (Hietanen E., et al., Dietand oxidative stress in breast, colon and prostate cancer patients: acase control study, European Journal of Clinical Nutrition 1994;48:575-586). Mean breath pentane concentration in the cancer patients(2.6 ppb, SD=2.8) was significantly higher than in the controls (0.6ppb, SD=1.1, p<0.01). They did not report concentrations of pentane inambient air, nor the alveolar gradients of pentane.

The methods and devices of the present invention can be particularlyuseful in diagnosing ischemic heart disease. There is an increasing bodyof evidence that myocardial oxygen free radical activity is increased inischemic heart disease. Oxidative stress also increases during surgicalreperfusion of the heart, or after thrombolysis, and it is related totransient left ventricular dysfunction, or stunning (Ferrari R.; et al.,Oxidative stress during myocardial ischemia and heart failure, Eur HeartJ 1998; 19 Suppl B:B2-11). Pentane was significantly increased in 10patients with acute myocardial infarction compared to 10 healthycontrols (Weitz Z W, et al., High breath pentane concentrations duringacute myocardial infarction. Lancet 1991; 337:933-35). However, afundamental flaw in the conventional breath pentane assays is that thecolumn employed in the gas chromatograph does not separate pentane fromisoprene, the most abundant compound in breath. The devices employed bythe methods of the present invention can separate pentane and isoprenefrom one another

Methods of the present invention can be used as non-invasive techniquesto diagnose organ rejection, including heart. There is a well-documentedbiochemical basis for breath testing that provides for the earlydetection of transplant rejection. Tissue damage arising frominflammation is accompanied by an accumulation of intracellular oxygenfree radicals (OFR'S) which cause lipid peroxidation of lipid membranes(Kneepkens C. M. F., et al., The hydrocarbon breath test in the study oflipid peroxidation: principles and practice. Clin Invest Med 1992;15(2):163-186. Kneepkens C. M. F., et al., The potential of thehydrocarbon breath test as a measure of lipid peroxidation. Free RadicBiol Med 1994; 17:127-60). This process is accompanied by the evolutionof alkanes which are excreted in the breath. One of these alkanes,pentane, is the best documented marker of OFR activity. Methods of thepresent invention can be employed to detect breath pentane in transplantrecipients.

End-stage renal disease (ESRD) is a fatal condition unless it is treatedwith either kidney transplantation or dialysis of blood or peritonealfluid. Clinicians who come into contact with patients with chronic renalfailure are familiar with the classic odor of uremic breath. It has beenvariously described as “fishy”, “ammoniacal” and “fetid”. This odorarises from presence of trimethylamine and dimethylamine in the blood,as well as increased concentrations of secondary and tertiary amines.Methods of the present invention can be used to detect these compounds,thus indicating the presence of ESRD.

Additionally, presence of methylated alkanes are common components ofthe breath in normal humans as well as in those suffering from lungcancer. Phillips M., et al., Variation in volatile organic compounds inthe breath of normal humans. Journal of Chromatography B 629 (1-2):75-88; 1999; Phillips M., et al., Volatile organic compounds in breathas markers of lung cancer: a cross-sectional study. Lancet 353:1930-33;1999. These VOCs appeared to provide additional markers of oxidativestress. Methods and devices employed by the present invention can beused to create patient's methylated alkane profile and thus serve asadditional tool in early lung cancer diagnosing.

Various personal odors may be detected in practice of the invention,such as breath or arm pit or the like. In another embodiment, thepresent invention is a breath test which can be used to determine thecharacteristic of metabolism of a drug in a subject. Specifically, thepresent invention can be used to determine this characteristic ofmetabolism by measuring the concentration of a metabolite in the exhaledbreath of the subject after an appropriate amount of the drug has beenadministered to the subject. Hereinafter, the term “characteristic ofmetabolism” includes whether such metabolism occurs, the rate ofmetabolism and the extent of metabolism. However, for clarity theaforementioned and following descriptions specifically describe themeasurement of the rate of metabolism. Generally, these tests involvethe administration of a substrate to the subject and the measurement ofone or more cleavage products produced when the substrate is chemicallycleaved.

For example, detecting Helicobacter pylori, which produces a largequantity of the enzyme urease, can be accomplished by orallyadministering urea to a subject with subsequent monitoring of theexhaled dioaxide and ammonia.

Breath tests can be used to measure physiological processes such as therate of gastric emptying. For example, gastric emptying rates weremeasured for solids and liquids by using octanoate or acetate as thesubstrate (Duan, L.-P., et al., Digestive Diseases and Sciences, 1995,40:2200-2206). The substrate can be administered to the subject and theexhaled breath of the subject was measured with an ion-mobilitydetection device.

The breath test of the present invention can be performed as follows.First, the drug is administered to the subject. Next, the exhaled breathof the subject is analyzed after a suitable time period for aconcentration of a metabolite of the drug, the concentration indicatingthe rate of metabolism of the drug in the subject. Such a breath testhas a number of advantages over conventional methods for determining theconcentration of a drug in the subject. Not only is a breath testnon-invasive, it is also more rapid than analyzing blood samples and itcan also be performed multiple times on the subject.

In one embodiment, the present invention provides a method and apparatusthat can measure and analyze components released from food or otherproducts during oral processing. An optional step of volatilization isemployed should detection of non-volatile components is desired. Thismethod can be used to measure components that are present in smallconcentrations, yet are important to the flavor of a product.

Illustrative embodiments of breath sample collection techniques will nowbe described. In one embodiment, the collection system included amouthpiece and a tube for carrying the exhaled breath of the subjectinto a mixing chamber. A sample outlet and exit tube connected themixing chamber to a measuring device, such as DMS detection device. Inaddition, heat can be applied to the system to prevent condensation ofmoisture from the breath sample on the system components. The mixingchamber can be provided to insure that the exhaled breath sample mixedwith previous samples, and that a small quantity of the combined breathsample was drawn from the chamber into the measuring device.

In another embodiment, the collection system uses a pumping system todraw an air sample from the nose of a subject, through a nose-piece andpast a membrane separator fitted to a DMS detection device.

In yet another embodiment, a carrier gas, e.g. N₂, and a breath samplecan be injected into a separating column, e.g. GC, and then circulatedtoward an ion-mobility detection device.

In another embodiment, the collection system described in U.S. Pat. No.5,479,815. In this system, the subject exhales a breath sample into oneor more collection chambers that are preferably maintained in atemperature controlled cabinet to prevent condensation of portions ofthe sample. Either mouth-exhaled or nose-exhaled air can be collected.Where food flavorings are being detected, samples are preferablycollected from the subject's mouth. Each breath sample can be purgedfrom its collection chamber with a non-reactive gas flow into a trapcontaining an interface that separates and collects components from thebreath sample. This interface preferably is an inert adsorbent materialselected for its ability to. A substrate coated with an absorbent orother material capable of collecting components may also be used. Theinterface, in addition, preferably permits any moisture contained in thebreath sample to pass through the trap, leaving only the collectedcomponents on the interface.

The adsorbent trap is then transferred to a thermal desorber or otherdevice capable of releasing the adsorbed components from the interfacesurface into a measuring and analysis apparatus, such as an ion-mobilitybased detection device of the invention. In one embodiment, thecomponents collected by an adsorptive trap are thermally desorbed fromthe trap and flushed into a gas chromatograph by a non-reactive gas flowprior to being identified by an ion-mobility detection device.

In another embodiment, the subject blows each breath sample firstthrough a condensation trap and then into the collection chamber. Thecondensation trap captures relatively non-volatile flavor componentsthat might not otherwise be recovered from the collection chamber orcould not be readily desorbed from an adsorbent trap. The condensationtrap preferably includes non-reactive glass tubing packed with anon-reactive and non-adsorbent substrate, such as glass wool. Othermaterials may be used provided that the materials withstand hightemperatures and do not react with flavor compounds. The trap ismaintained at a temperature that will encourage the condensation on thesubstrate of slightly volatile or relatively non-volatile flavorcomponents in the subject's breath and permits the volatile componentsto pass through into the collection chamber.

The condensation trap is then heated to re-vaporize the condensedcomponents, so that they may be purged into measuring and analysisdevices such as a gas chromatograph and mass measuring device.Similarly, the flavor components that passed through the condensationtrap into the collection chamber also may be flushed into an adsorbenttrap so that they may be studied as discussed above.

Quality Control of Foodstuff and Food-Processing Surfaces

The present invention can be used in the detection of chemicalcontaminants and/or viable pathogens that may be present in processedfoods, such as found in ground beef and other meats. The ability torapidly confirm or disprove the presence of significant contaminationmay, for example, reduce or eliminate the need for destruction or recallof ground meats or other foods in cases where contamination was possiblebut not certain by demonstrating that the meats or other foods inquestion are not contaminated with viable bacteria at the time oftesting.

The present invention can be used in food processing plants, hospitals,laboratories, and other facilities to determine whether surfaces arefree of pathogens or whether additional or more stringent sterilizationor containment procedures are required. This can be achieved by, forexample, collecting a sample of dust or a cotton swab of a surface inquestion, followed by either re-suspending the sample material in afluid or immediate volatilization. The volatilized sample is subjectedto detection as described herein.

The present invention can further be used to identify contaminated foodcontainers by collecting either a sample of a headspace or a swab of asurface.

In one embodiment, the present invention can be used for detection ofsubstances in a foodstuff industry. Both odorous (relatively volatile)and non-odorous substances (relatively non-volatile) can be detected,the latter with an additional optional step of volatilization beingrequired before the sample being directed into a DMS device.

The detection of odorous substances has many industrial applications,especially in processes in the foodstuff industry, in which one can, forexample, determine the degree of freshness and the quality of theproducts, due to the odorous substances which they release. Gaschromatography, which consists in a method of separating the moleculesof gas compositions, can be used as a way of pre-separating componentsof a sample prior to detection by DMS.

A method for detecting odorous or volatile substances or substances madevolatile, comprises the steps of directing an air sample collected inthe proximity of a food substance or a food-handling surface to DMSdetection device.

This method can advantageously employ sample collection techniquesdescribed in U.S. Pat. No. 5,801,297. In particular, the transport ofthe odorous substances from a sample can be achieved by a variablecontrolled flow of gas. This allows for very rapid detection of odoroussubstances, in about a few seconds. The means used in order to achievethis variable controlled flow of gas are advantageously made up of atleast a pump with variable flow rate. During the phase of separating anddetecting the components of a sample, the gas flow rate can bediminished or increased according to whether the substances become moreor less volatile throughout the duration of the measurement period.

Smart DMS Smoke Detector

The present invention can be used for identification of a fuel source byanalyzing smoke. Where a gas chromatography device is used topre-separate the smoke components, GC-DMS instrument operating atambient pressure in air provides a compact and convenient fuel-specificsmoke alarm at a reasonable cost. The specificity and sensitivity of thesystem earns the moniker of a “smart DMS smoke detector”.

One embodiment of the present invention provides a smart smoke detectorwith high specificity by detection of volatile organic constituents(VOCs) in the smoke. Fires produce a large number of organic compoundsin complex mixtures in the vapor phase as seen in fires from syntheticpolymers, cigarettes, and cellulose-based materials such as wood orcotton. This approach provides sufficient analytical information forselective detection of fire components through measurement of thechemical composition of the emissions.

Illustrative Differential Ion Mobility Devices of the Present Invention

An illustrative practice of the invention is shown as system 10 in FIG.1, in which a sample A and transport fluid B are delivered to a filter C(operating by aspects of ion mobility), wherein the ionized sampleS^(+/−) is filtered by ion species according to aspects of ion mobility.Thus a selected ionized species is outputted from the ion filter(“separator”) and may be further processed in part D. This furtherprocessing may include being detected to indicate presence of abiological material in the sample, and/or may include being collectedand used as a biological material extracted from the sample. The sampleitself may be delivered already including ion species of interest.

The sample is ionized in ionization region E before it enters the filterpart C. In one alternative embodiment, region E receives the sample andtransport fluid where they are mixed together in mixing region E1 inpresence of an ionization source E2, or are mixed with an additionalionized fluid flow from source E2, all to provide the ionized sampleS^(+/−) that is delivered from region E to filter C. Filter C ispreferably a DMS filter.

In a preferred illustration of the invention, an analyte is detectedbased on differences in mobility of the ionized analyte in a DMSelectric filter field. Preferably, this field analysis includes highfield asymmetric waveform ion mobility spectrometry-type differentialion mobility, as described in U.S. Pat. No. 6,495,823 or U.S. Pat. No.6,512,224, and generally described herein as DMS. These patents teachboth gas transport of ion species and electric field ion transport ofion species, which may be practiced in embodiments of the presentinvention.

In one practice of the invention, a DMS filter (separator) is tuned topass a specific analyte of interest, and the passed analyte is thencollected or processed accordingly. In another practice, the filterfield is scanned through a range that enables detection andidentification of a range of ion species that are present in the sample,including positive and negative species. This spectrum can be detectedfor a full characterization of the detected sample.

A further practice of the invention is shown in FIG. 2A wherein system10 includes separation sections “S-A” and “S-B” followed byidentification section “ID”. In operation a complex sample S* can beseparated in first section S-A and the separated sample flow S is thenapplied to the second section S-B for further separation/processing. Theresult of both separations and the related S-A and S-B data iscorrelated and enables reliable identification of separated componentsfrom the complex sample. The output of section S-B is evaluated in theidentification section ID.

It will be understood that a preferred process of the invention includesusing DMS to generate separation data and at least one other processingstep that yields its own separation data. This additional separationstep may be before or after DMS filtering. The combination of detectiondata leads to highly reliable identification of ion species present in acomplex sample even at trace levels. In a preferred embodiment, thefirst separation section S-A includes a gas chromatograph (GC) and thesecond section is a DMS filter.

Accordingly, in one embodiment, the present invention is an apparatusand a method for detection and identification of analytes in a sample byaspects of ion-mobility based detection. In this embodiment, a portionof a sample is directed into a first separation device, therebyobtaining a first profile of a sample. A portion of a sample is alsodirected into a second separation device thereby obtaining a secondprofile of a sample. At least one of the first and the second separationdevices is a DMS device. As used herein, a “profile” includes any dataobtained by a separation device, such as, for example, any ion-mobilitysignature, such as DMS mobility, time of flight, mass spectra,chromatographic retention time and the like. One skilled in the art willdetermine specific data comprising a profile based on the nature of thesample to be analyzed and the separation device employed by a specificembodiment of the apparatus and a method of the present invention.

The first and the second profiles obtained above are combined, therebyallowing identification of at least one analyte in a sample. Thecombination of profiles can be done by way of comparison of the twoprofiles, whereby the presence of a particular analyte can be confirmed.The combination can further include adding the data obtained by a firstseparation device to the data obtained by the second separation device.

The DMS practice of the invention may include a DMS filter in either orboth separators S-A or S-B. A preferred DMS system is shown in FIG. 2B,including a sample input section 10A, a DMS ion filter section 10B. TheDMS output is evaluated in the detection and identification section 10Cin FIG. 2B (which constitutes the identification section ID of FIG. 2A),which includes an intelligent controller/driver provided by command andcontrol unit 34.

Typically, a memory or data store 33 is used to record separation ormobility signatures for known ion species and the apparatus is enabledwith this data. The DMS detection data can be correlated with the fieldconditions data (e.g., RF characteristics, compensation, flow rate,temp., etc.) and forms a detection dataset for the detected ion. Thedetection dataset is compared to a signature dataset(s) for known ionspecies as stored in the data store. A match enables identification ofthe species of the detected ion. In one embodiment, the data storeincludes associated characteristic retention time data and data thatrelates to use of other separation techniques (such as a thermallycontrolled SPME prefilter).

The detection is both qualitative and quantitative. For example, upondetection of an ion associated with an anthrax molecule, a match withthe stored data will enable identification of the detected species as“anthrax” and with an indication of detection level based on theintensity of detection. Such an indication may be issued as a warning toa display or other output device.

The DMS RF signal is generated and the compensation bias is applied tofilter electrodes 20, 22 by drive circuits 32 within command and controlunit 34. Preferably a detector 26 is provided, and preferably a chargedetector (e.g., Faraday type detector), including detector electrodes28, 30. As ions contact they detector electrodes they deposit theircharges and these detection signals are then amplified by amplifiers 36,38, all under direction and control of unit 34. Preferably a computer ormicroprocessor 40 correlates drive signals applied to the filterelectrodes with detection signals from amplifiers 36, 38, and makes acomparison to stored data in data store 41, and then issuesidentification data 42 to a readout device, such as for indication ofdetection of the target molecule.

In one embodiment, a GC output of section S-A delivers sample S as aneluant that is carried by a drift or carrier gas G into flow channel 11at inlet 12. The sample S flows toward a sample outlet 13 at the otherend of flow channel 11. Sample S may include various molecules includingtrace level analyte T. The sample may be delivered directly from the GC(or in other embodiments may be delivered via a nebulizer, spray head,etc.), and flows into ionization region 14. Molecules in the sample arethen ionized by ionization source 16.

The result of ionization is ionized analyte ions T+/− and other ions S+,S− with some neutral molecules S°, as may be derived from variouschemical species that are in sample S. These ions may appear asmonomers, dimers, clusters, etc.

The ions and neutral molecules is flowed into the ion filter section 10Bfor analysis. The carrier gas carries the ionized sample into theanalytical gap 19 formed between electrodes 20, 22 of filter 24. In apreferred embodiment of the invention, filtering proceeds based upondifferences in ion mobility in an asymmetric RF filter field alternatingbetween high and low field values. This filtering reflects uniquemobility characteristics of the ions as species; the process enablesdiscrimination of species based upon mobility characteristics in thefield which reflects ion size, shape, mass, charge, etc.

In accordance with an illustrative embodiment of the present invention,an asymmetric field voltage, Vrf, applied across the filter electrodes20, 22 generates a field F (e.g., 10,000 V/cm) whose strength alternatesbetween high value Vmax and low value Vmin. This variation in the fieldstrength causes the ions to move transverse to the sample flow in theflow channel, with the transverse motion being representative of thecharacteristic field mobility of the ions.

The mobility in the high field condition differs from that of the lowfield condition, and this mobility difference produces a net transversedisplacement of the ions as they travel longitudinally through thefilter field between the electrodes, resulting in an ion trajectory overtime. This trajectory will drive the ions into the filter electrodes,causing them to be neutralized, lacking a countervailing compensation.

A compensation, such as a DC compensation voltage Vcomp, is applied tothe filter to differentially compensate this transverse motion. Thecompensation will compensate the transverse motion of a selected ionspecies and will cause it to return to the center of the flow path basedon its compensated mobility characteristics. Thus this returned ionspecies is able to exit the filter without colliding with the filterelectrodes and without being neutralized.

In this process other species will not be sufficiently compensated andwill collide with the filter electrodes 20, 22 and will be neutralized.The neutralized ions T° are purged by the carrier gas, or by heating theflow path 11, for example.

A compound may be represented by either or both positive and negativeions (“modes”) such as T+ and T−, as such modes may be generated byionization of the analyte molecules T. In a preferred embodiment, bothpositive and negative modes of an ionized species can be simultaneouslydetected in detection and identification section 10C. In this case,detector 26 includes biased detector electrodes 28, 30 that are capableof simultaneous detection of modes simultaneously passed by the DMSfilter.

The in-line configuration of the flow path enables both modes of aspecies generated during ionization to flow into the DMS filter 24. TheDMS filter passes these modes during a mobility scan, where each is thepassed species when the scanned field conditions are appropriate. Thusanalyte T may produce ions T+ and T− which each will pass through thefilter at the appropriate signature field conditions.

In practice of the invention, ion species are filtered based on mobilitydifferences. Therefore in a preferred practice of the invention, allions of an ion species will be passed on for detection, whether positiveor negative ions, and which may be detected simultaneously. Accordinglythe detector electrodes are biased so that one attracts the positive andthe other attracts the negative ions. Thus, in an embodiment of sucharrangement both “positive mode” and “negative mode” ions of a speciesare detected simultaneously. Having both modes from a single detectionprovides a more unique signature for the detected ion species andtherefore increases the potential accuracy of species identification ofthe invention. The benefit of mode detections is further discussedbelow.

In a practice of an embodiment of the invention, the ions flow to thedetector wherein electrode 28 may be biased positive and electrode 30biased negative, and therefore electrode 28 steers the positive ions T+toward electrode 30, and results in ions T+ depositing their charges onelectrode 30. Meanwhile, electrode 30 acts as a steering electrode andsteers the negative ions T− toward electrode 28, and results in ions T−depositing their charges on electrode 28. It is a feature of thisembodiment that both + and − ion modes may be detected simultaneously.Single mode or dual mode detection data is combined with filter fieldparameter data and is then compared to stored data to make anidentification of the detected analyte T, and this is combined with theseparation data representing the first separation to enable highlyreliable identification of the analyte of interest, even at tracelevels.

In accordance with the present invention, discrimination of ions fromeach other according to mobility differences is achieved wherein the RFfield and the selected compensation enables a particular ion species topass though the filter. A plot of detection intensity versuscompensation for a given field strength is shown in FIG. 2C, where peaksTa, Tb indicate intensity of the detection signal at compensation levelsa, b for the particular RF field. Peak “Ta+” represents the “analyte Ta”positive mode, and peak “Tb+” represents “analyte Tb” positive mode.Peak “Tb−” represents “analyte Tb” negative mode. The intensity of thepeak may be correlated with detection quantity. Furthermore, theretention time associated with these peaks can be correlated with thepeaks to improve reliability of species identification.

In a simplified aspect of the invention, a first separator S-A (e.g., afast GC) is coupled with to a second separator S-B (e.g., DMS filter),as in the arrangement of FIGS. 2A and 2B. In a preferred embodiment, apre-filtering step is provided by a front-end collector system S-C(shown in dotted outline) to enable a highly reliable, selective andsensitive advanced chemical detector system. In practice of theinvention, various analytes that are difficult to discriminate anddetect can be identified with confidence.

For example, the sample can be collected, such as by means ofsolid-phase micro-extraction (SPME) media, in pre-collector part S-C,and then delivered to a GC, in separator S-A, for further separation andfollowed by DMS separation in part S-B and species identification inpart ID, according to the invention.

SPME uses a fiber or tube having coating material which preferentiallyadsorbs analytes from a sample matrix and delivers the analyte forfurther processing. SPME is routinely applied to gas-phase liquid-phaseextractions, such as for extracting organic analytes from a sample anddelivering same for chromatographic analysis. The preferred embodimentenables delivery of a volatilized or volatilizable sample which can beprocessed in gas phase.

Embodiments of the present invention enable provision of intelligentmonitors for a variety of application. For example, smart air monitors,smoke detectors and the like can be provides. Programmable control ofthe separation sections or selection of dedicated components enablestailoring a system to particular needs. An illustrative embodiment ofthis invention enables an advanced environmental detector of reasonablyhigh analytical performance. In this embodiment, a SPME collector system100, shown in FIG. 3, which provides a pre-filter front-end (seeseparation section S-C) and delivers sample S to the GC (separationsection S-B) and then the DMS section S-B proceeds as described.

The SPME collector system 100 preferably has several SPME collectors101, 102, 103 . . . n. which are selected for special characteristics.For example, all may be designed to selectively deliver a particulartype of analyte or a range of analytes into collector 110.

The SPME fibers introduce the sample S into collector 110. In oneembodiment, a drift gas 112 is introduced into collector 110 and carriesthe sample S introduced by the SPME fibers to the separator S-A (e.g.,GC). Now further separation, filtering, detection and identificationproceeds as earlier described.

This SPME sampling may include the step of heating the SPME fibers topurge VOCs, or to pyrolyze/volatilize a sample that then is deliveredinto collector 110 and then for further processing such as by GC-DMS.The heating may be provided by heaters 116 associated with the SPMEabsorber fibers 101, 103, 105, etc. The system is controlled bycontroller 34.

The heaters may be switched on and off and in this manner can controlsample delivery within a desired range of chemical compounds accordingto the characteristics of the switched SPME fibers. For example, upondetection signal, one or a series of the fibers 101-n can be heated tochange the sample absorption profile and delivery characteristics.Heaters 116 can also be used to heat the fibers for purging of same oreven for pyrolysis of the samples. Such heating can be ramped to createa desired profile.

In one embodiment, the present invention provides detection of smoke andintelligent discrimination of components in the smoke. The chemicalcomposition of smoke from sources of interest exhibit measurablechemical differences that can be analyzed by the SPME-GC-DMS system. Aremarkable level of reproducibility for complex chemical process (i.e.,combustion of natural materials) was obtained using simple samplingmethods. In a further embodiment, monitoring changing vapor compositionwith time of burn and detailed identification of volatile products fromcombustion is used in an augmented method of the invention.

It will be appreciated that the present invention is not limited todetection/discrimination of smoke. More broadly, the present inventionenables analysis of compounds by including differential ion mobilityanalysis in compensated high field asymmetric waveform ion mobility RFfields in a compact package that can be manufactured using high volumetechniques that result in low per costs and yet produces resultscomparable to expensive analytical equipment. Systems according to theinvention can be light-weight and yet provide the ability to providehighly effective analytical equipment whether in the field or in thelaboratory.

Devices of the invention are able to rapidly produce accurate, real-timeor near real-time, in-situ, orthogonal data for identification of a widerange of chemical compounds. Devices of the invention, such as devicesaccording to FIG. 2A through 2C and FIG. 3, enable distributedinstallation of detection systems such as can serve heating and airconditioning systems (HVAC), where air quality monitoring and/or flowcontrol and mixing of interior and outside air is of interest. Such HVACsystem can be controlled by a central controller (e.g., controller 34),to meet user needs automatically or on demand.

DMS devices of the invention may incorporate various electrodeconfigurations, including coaxially or non-coaxially cylindrical,curved, curvilinear, arcuate, radial, plate, parallel, planar or flat.These configurations may be focusing or non-focusing as practiced in DMSdevices. A preferred practice of the present invention is generallyreferred to as “plate-type”, and it will be understood embodiments mayuse facing electrode portions, segments, sections, or plates. In oneembodiment, non-uniform focusing fields are generated between the DMSfilter electrodes; such embodiment may include a curved flow pathincluding flat, non-flat or curved DMS electrodes.

Turning now to FIG. 4A and FIG. 4B, alternative embodiments ofelectrodes 20 and 22 are shown. As shown in FIG. 4A, filter electrodes,labeled 20′ and 22′, can be coaxially cylindrical. In anotherembodiment, shown in FIG. 4B, either one or both electrodes, labeled 20″and/or 22″, can be curved or curvilinear. In particular, segments 20Acan be curved, thereby producing a focusing effect known in the art, orstraight, thereby producing a field substantially similar to thatproduced by the electrodes 20 and 22 as shown in FIG. 2B. In theembodiment where segments 20A are straight, their length can bevariable.

Device for Detection of Analytes in a Volatilized Sample

In one embodiment, the present invention is an apparatus for detectionand identification of analytes in a volatilized sample using themobility-based signature obtained by a differential ion mobilityspectrometry (DMS) device.

Referring to FIG. 5, an illustrative pyrolysis-based DMS system deviceof the invention will now be described. It is understood that any of thevolatilization techniques described herein can be adapted for use withthe instant invention.

In this embodiment, system 100 includes a sampler or other particlecollector 102 which delivers liquid or solid sample to a pyrolyzer 104(such as a commercially available pyrolyzer from CDS Analytical) whichhas an output coupled to the flow path 106 of the DMS analyzer 110. Theflow path structure (sometime referred to as a drift tube) has an inlet112 for receipt of the pyrolyzed sample output from the pyrolyzercarried by carrier gas 114. The pyrolysate in transferred from thepyrolyzer to the DMS through a sealed and heated interface. Duringsample loading on the probe, the pyrolysis chamber is purged while astream of clean N2 is diverted into the DMS. During pyrolysis, the flowsare diverted through a valve into the analyzer to assist introduction ofthe pyrolate.

In one example, the pyrolyzer heated samples from room temperature to1400 C at rates from 10-20° C./msec. The controlled temperature rampingenables selective desorption of compounds from the probe, thereforeenhancing resolution and signal-to-noise of the apparatus. A dryingfunction evaporates and vents the solvent out a purge vent resulting insample concentration and prevention of the solvent from entering the DMSanalyzer 110. A probe cleaning function, flash-heats and desorbsleft-over sample between analyses.

The pyrolate is carried by the carrier gas into the ionization chamber120 where source 122 ionizes the sample. The ions (“+”, “−”) are carriedby the carrier gas into the filter 124 between filter electrodes 126,128. In a preferred practice of the invention, an asymmetric high-lowvarying RF field is generated between the filter electrodes, withapplied DC compensation, under control of controller/driver 130. Ionspecies are passed to the detector 132 based on compensated fieldconditions and mobility difference for the species. As the compensationis scanned, a spectrum can be recorded for the sample. Detector 132includes electrodes 134, 136, which enable detection of positive andnegative modes for each species.

In a preferred embodiment, electrodes 124, 134 are formed on a substrate140 and face electrodes 126, 136 formed on substrate 142. Preferably thesubstrates are insulating. The substrates are mated to fix the distancebetween the electrodes and defining the analytical gap G between theelectrodes (preferably ˜0.5 mm). The asymmetric field is generatedbetween these electrodes transverse to the analytical gap and the ionsare flowed in the gap through the field.

Additional Illustrative Embodiment of Dms Practices of the PresentInvention

Referring now to FIG. 6, an alternative separation method and apparatusof the invention is shown. In this embodiment, a dual channel system 300includes a first flow path 11 and a second flow path 311. As the ionsare separated by passing through filter 24 in flow path 11, they aredeflected by deflector electrode 320 into a detector 326. The deflectorelectrode 320 is disposed substantially at the output of a flow path(here, a first flow path 11) of a differential mobility spectrometry(DMS) device. Preferably the detector may include a detector electrode327 which also can be biased to act as an attractor electrode 327 incombination with the deflector 320. In a non-limiting example of theoperation of this embodiment, positive ions (T⁺) will be deflected by anegatively biased deflector 320 and positively biased attractor 327,while a negative ion (T⁻) will either continue along its original pathor will be neutralized on a negatively charged deflector electrode 320.In one embodiment, as the ions strike the detector electrode 327 theircharges are registered and generate a detection signal. Now detectionspectra can be generated as needed. In the embodiment of FIG. 6, theions are separated from the rest of the flow out of the filter 24 inflow path 11, and by means of the deflector, a refined set of ionspecies of interest is detected and/or obtained. As this species isneutralized by contact with the detector electrode they pass out of thedetector/collector as a purified set of molecules which may be used as acollected sample, may be re-ionized and reprocessed, or the like.

It will be further appreciated that in embodiments of the invention,detections are made and then the identification process typicallyinvolves comparison against a lookup table of stored detection data.Thus a practice of the invention not only results in detection of amarker but also results in indication of the analyte with which themarker is associated. For example, if bacterial spores were in a sample,the above detection results would be obtained and would be comparedagainst a store of related detection data. Upon a positive match, anidentification announcement would be made.

Preferably, the apparatus of the invention includes an on-boardvolatilizer portion and DMS analyzer, wherein collected samples arevolatilized and then resulting gas sample is automatically transportedto the analyzer and then detected for evaluation of presence of analytesin the sample based on ion mobility signatures. In a further embodiment,the volatilizer and DMS device may be made in a single package. Thesample collector may also be on-board.

In a further embodiment of the present invention, a sample is identifiedby a multi-stage analysis, wherein a first stage filters a sample byparticle size and defines a narrowed sample set, and in a second stagethis sample is pyrolyzed and then analyzed based on high field ionmobility as discussed. Results of the first and second stage arecorrelated with known standards to identify the compounds in the sample.

Multichannel (Array) Detection

Devices suitable for practicing the methods of the present invention aredescribed in U.S. Pat. No. 6,495,823 and U.S. Pat. No. 6,651,224, andinclude teaching an array of DMS filters. An illustrative devicecomprises a housing defining at least one flow path between a sampleinlet and an outlet, a plurality of ion filters disposed within thehousing, each ion filter including a pair spaced filter electrodes, andan electrical controller for applying a bias voltage and an asymmetricperiodic voltage across each pair of ion filter electrodes forcontrolling the path of ions through each filter. In one embodiment, thedevice provides an array of filters, each filter associated with adifferent bias voltage, the filter may be used to detect multipleselected ions without sweeping the bias voltage or, in an alternativeembodiment, by simultaneously and independently sweeping the biasvoltage in different ranges and at different fields. Filters may be inparallel or in series with one chemical sample processing throughmultiple ion filters.

The teaching of the above-referenced disclosures are incorporated hereinby reference in their entirety.

EXEMPLIFICATION Example 1 Endospore Biomarker 2,6-Pyridine-DicarboxylicAcid (Dipicolinic Acid) is Detected by a DMS Device and Bacillus SporeBiomarkers are detected by a DMS Device after Pyrolysis.

Pyrolysis of bacterial spores from species such as Bacillus andClostridium produces large quantities of gaseous,2,6-pyridine-dicarboxylic acid (dipicolinic acid or DPA) as uniquemarker, which may then be detected by a gas chromatography/DMS device.Typical spores contain roughly 5-15% dry weight of DPA (MW=167), whichis speculated to provide the spore with heat resistance. While thepresence of DPA does not signify with certainty that an infectious agentis present in the environment, a sudden increase in its concentrationcan serve as a trigger for initiation of a target-specific search.

The commercially available pyrolyzer PyroProbe1000 was acquired from CDSAnalytical with the necessary functions to handle the introduction ofliquid and solid samples into the DMS detector. The pyrolyzer is capableof heating samples from room temperature to 1400° C. at rates from 1 to20° C./s. The controlled temperature ramping enables selectivedesorption of compounds from the probe, therefore enhancing resolutionand signal-to-noise of the DMS. A drying function evaporates and ventsthe solvent out a purge vent resulting in sample concentration andprevention of the solvent from entering the DMS filter. A probe cleaningfunction, flash heats and desorbs left-over sample between analyses. Thepyrolate is transferred to the DMS through a sealed and heatedinterface. During sample loading on the probe, the pyrolysis chamber ispurged while a stream of clean N₂ is diverted into the DMS. Duringpyrolysis, the flows are diverted through a 6-port valve into the DMSfor introduction of the pyrolate into the DMS.

In order to provide a control result for comparison with data obtainedusing the DMS unit, a B. subtilis sample was analyzed usingpyrolysis-ion trap mass spectrometry. The concentration of the B.subtilis sample was 10′ organisms/ml. This experiment (FIG. 7) showedthat the expected biomarkers and both DPA and picolinic acid (PA) wereevident in the endospore spectra. Other unidentified biomarkers werealso measured using this technique as shown in the background spectralpeaks. We further tested the ability of the DMS to detect endosporebiomarkers by using both DPA and PA standard solutions.

FIGS. 8 (dual mode), 9 (dual mode) and 10 (single mode) provides spectrafor PA and DPA obtained from solid samples pyrolyzed sequentially anddetected in a DMS system of the invention. Picolinic acid was pyrolyzedthrough a temperature excursion of 130 to 300° C. at a rate of 20,000°C./s, the interface temperature was held at 130° C. Dipicolinic acid waspyrolyzed from 145 to 400° C. at 20,000° C./s, the interface temperaturewas held at 145° C. Both PA (100 ppm) and DPA (100 ppm) produce positiveand negative ion peaks that can be used for identification. In addition,pure DPA produces a secondary positive ion peak, further differentiatingits fingerprint pattern. The peak width at half height averages 1.4 V.It is known that pyrolysis is capable of fully decarboxylating DPA topyridine. Ideally, controlled and more gradual pyrolysis conditions willlead to loss of only one carboxylic acid group to generate PA, enablingspecific identification of the DPA source as bacterial spores. Due tothe volatility of pyridine, pyrolysis was not necessary forintroduction, and the interface temperature was held at 130° C. As seenin the DMS spectra, pyridine does not produce negative ions. The absenceof a negative ion peak enables one to conclude that the pyrolysisconditions employed are mild enough to prevent full decarboxylation andthat pyridine can be differentially detected.

FIG. 11A shows the full DMS spectrum of pyrolyzed B. subtilis spores asa simulant for B. anthracis. The spores were suspended in dH2O at aconcentration of 2.4×109 spores/ml. The spores were diluted to 100,000spores in 1 μl, and the sample was dried and pyrolyzed through atemperature excursion from 250° C. to 400° C. at 20,000° C./sec with theinterface temperature at 250° C. FIG. 1A shows the time course of theDMS spectra after pyrolysis is initiated. The signal is complex andchanges over time, indicating a large number of potential biomarkertargets. There is a large prominent peak as well as low amplitudeclusters of “noise” in the spectra. The prominent peak may be acomplexed form of DPA or PA released during pyrolysis, although exactchemical identification is not possible. The DMS signal may also containtwo components in the low amplitude signal: electronic noise, and tracelevels of organic volatile compounds. FIG. 1B shows a time course ofboth the positive and negative DMS spectra at 10 seconds after the onsetof pyrolysis. Both spectra show biomarkers are detected. These resultsshow the DMS is capable of detection of known endospore biomarkers.

Example 2 Monitoring Food Quality

Chemical changes in the living system or degradation processes of cellsafter death are accompanied by the formation of molecular byproducts.These processes include the breaking down of peptides and DNA strands tosmaller components, and changes in amino acids that lead to theformation of amines. One of the processes of particular interest is thebreakdown of amino acids and the production of diamines and polyamines.

Furthermore it is known that bacterial decarboxylation of ornithine andlysine produces putrescine and cadaverine respectively. An atmosphericpressure ionization method of the invention is particularly suited forthe detection of these markers, such as biogenic amines, since they tendto have either high proton affinity and form stable positive ions orhigh electro-negativity and readily form negative ions that are detectedin a DMS system of the invention.

FIG. 12 shows DMS spectra detected according to a food-qualityembodiment of the invention for a mixture containing both putrescine andcadaverine. The putrescine peak at about −30 volt compensation is wellseparated from the cadaverine peak at −29 volts, and which are separatefrom the detected n-Nonylamine. Based on these results, it will beappreciated that a food-quality detector of the invention can be used toevaluate the quality of a food sample, such as meat, based on thedetected presence and intensity of these bio-markers.

Example 3 Breath Analysis

Another application of the invention is in breath analysis. The humanbreath contains over 400 organic compounds at concentrations typicallyin the parts-per-million (ppm) to parts-per-billion (ppb) range. Only aslender barrier, the pulmonary alveolar membrane, separates the air inthe alveoli of the lung from the blood flowing in the capillaries. Thismembrane allows volatile organic compounds to easily diffuse from theblood into the breath. Moreover, the concentration of these compounds inthe breath can be correlated to their concentration in the blood, asnoted through the widespread use and acceptance of a breath analyzer todetermine alcohol consumption.

Through systematic studies, concentrations of particular compounds havebeen correlated with specific diseases or impairments in metabolicpathways. However, while these studies are encouraging, there are stilla number of complicating factors which have limited wide spread adoptionof breath analysis for medical diagnosis. These include: the complexityof current breath analysis systems, their high cost, amount ofcorrelation between the data and disease, and the complexity of dataanalysis due to interferences and moisture.

In practice of the present invention, a non-invasive DMS breath analysissystem is provided. In one set of experiments, sample collectioninvolved collecting a breath sample directly onto a solid phasemicro-extraction (SPME) fiber assembly. The SPME fiber was placed inproximity to the mouth of the subject and the sample collected for twominutes. The SPME assembly was coupled to a GC injector port which washeld at 120C and desorbed the sample from the fiber into the GC column.The present wide-spectrum DMS was attached at the detector port of theGC for DMS filtering and species identification of the GC elute.

A background baseline spectra without sample on the SPME fiber is shownin FIG. 13. Spectra from subject #1, FIG. 14, and subject #2, FIG. 15,are very similar except for the peak at a compensation of about −3 voltsfor specimen #2. Using the GC alone, without the benefit of the presentinvention, the presence of these different compounds would not beevident. The resultant GC-DMS plots shows the chromatographic retentiontime on the y-axis and the compensation voltage plotted on the x-axisand shows the value of the detector in providing additional informationto simplify and assist in the analysis of a human breath sample, as aviable practice of the present invention. However it also should benoted that in practices of the invention direct sampling and analysis byDMS can be practiced without SPME.

Example 4 B. Subtilis Spores Detection

As shown in FIGS. 16A-C, spectra for markers from pyrolyzed B. subtiliswere identified. Spectral DMS scans for pyrolyzed water sample are shownin A, 40,000 spores pyrolyzed are shown in B, and 120,000 sporespyrolyzed are shown in C. A person skilled in the art will recognizefrom this data that markers at 1, 3 and 4 correlate with the presence ofspores, with amplitude corresponding to concentration.

Example 5 Analysis of Murine Urine Samples

In one experiment mouse urine samples were tested using DMS as shown inFIG. 17 showing positive DMS spectra. In the figure, a large carrier gas(N2) peak (˜3 a.u.) is seen at 0 Voltage Compensation (Vc), while urineheadspace (vapor) detection spectra is seen just to the left (<0 Vc).

In this demonstration, urine sample headspace vapor from three differentindividual B6-H-2b male mice was analyzed. The DMS spectra indicated theurine samples were similar to each other but different from two controlmonomolecular odorants (isovaleric acid and isoamylacetate). A smallnumber of sample preparation permutations were tested to identifyconditions that yielded the most volatiles as indicated by intensity inthe DMS spectra. Addition of: (1) water (to increase volume of urinesample), (2) salt (0.2 mg/μl), and (3) heat (37 C), all yielded morevolatiles.

It was possible to demonstrate use of DMS as a biological evaluationtool for medical diagnostics, such as for urinalysis. It is also notedthat such testing does not require fresh liquid samples. While freezingand thawing of such samples reduces the amount of volatiles, stilldetection can proceed. In practice of the invention, a data base ofurine and analyte samples can be determined and stored.

Further, a lookup function of a device of the present invention enablesidentification of ion species detected in urine. This experiment isillustrative of establishing baseline upon which a specific detector canbe established. For example, detection of such analytes as pronase,(NH₄)₂SO₄, KH₂PO₄—H₂O, CK2O3, K₂CO₃ or NaCl can be detected.

Example 6 Use of a DMS Device of the Present Invention as aChromatographic Detector

A DMS device suitable for practice of the present invention wasinterfaced to a GC and used as a chromatographic detector. The systemperformance was compared with the Flame Ionization Detector (FID). Theaverage FID detection limit was 2E-10 g, while a preferred DMS system ofthe invention had a detection limit of 2E-11 g. Furthermore, the DMS isflame-free.

Similarly to a mass spectrometer, the ion information provided by theinvention offers a second dimension of information to a GC chromatogramand the ability to enhance compound identification. FIG. 18 showsspectra according to a GC-DMS embodiment of the invention, with the partshown as a chromatogram (right frame) being typical of what is seen froma FID. In practice of the invention, the chromatogram is the sum of thepeak intensities for the product ions created. The associatedtwo-dimensional plot (left frame) of ion intensity (indicated bygradient) versus scanned compensation voltage provides a means offingerprinting the compounds eluted from the GC. Therefore practice ofthe invention provides three levels of information: retention time,compensation voltage, and ion intensity, all shown on the spectra ofFIG. 18. Furthermore, in a preferred in-line DMS system of the inventionsuch as taught in U.S. Pat. No. 6,495,823, spectra may be obtainedsimultaneously for positive and negative ions, i.e., dual mode,augmenting or eliminating the need of serial analysis under possiblychanging instrumental conditions, as required with other equipment.

As shown in FIG. 19, decreased GC runtime produced co-eluting speciesthat were subsequently resolved in the DMS spectra. In this way, a fastGC can be used while maintaining the required compound resolution.Furthermore, the reproducibility of the present invention compares verywell to that of the FID as shown in FIG. 20. FIG. 20 shows a comparisonof FID and DMS reproducibility for a homologous alcohol mixture.

Example 7 Parallel Analysis of Bacterial Samples using Pyrolysis/GASChromatography and a DMS, Flame Ionization and Mass SpectrometryDetection Devices

The py-GC/DMS analysis of bacteria showed a broad range of volatile andsemi-volatile organic compounds spanning molecular weights from 50 toover 250 amu. Information contained in the patterns of retention timeversus compensation voltage prove analytical value of the differentialmobility spectrometer. Products from the pyrolysis of bacteria werematched to known chemicals. The findings were also supported by parallelstudies using py-GC/FID and py-GC/MS.

Material and Methods

Detection Devices

Three gas chromatographs (Hewlett-Packard Co., Avondale, Pa.) wereequipped with a splitless injector, 15 m SPB-5 capillary column (ID 0.25mm, 0.25 μm film thickness, Supelco, Bellefonte, Pa.) and differentdetectors. Each of two HP model 5890A gas chromatographs was equippedwith a flame ionization detector or an HP model 5871 mass selectivedetector (MS). An HP model 5880A was equipped with a DMS analyzer asdetector. Experimental parameters for all gas chromatographs wereidentical and included: initial temperature, 50° C.; initial time, 2min; program rate, 8° C./min; final temperature, 250° C.; and finaltime, 5.50 min. Pressure on the injector ports was nominally 5 psig witha split ratio of 50:1 and was adjusted individually so retention timesbetween instruments matched. Split flow was −30 mL/min and septum purgewas 3 mL/min. Bottled nitrogen (99.99%) was used as carrier gas for theGC/FID and GC/DMS. Helium (99.99%) was scrubbed over a Hydrox PurifierModel 8301 catalytic reactor (Matheson Gas Products, Montgomeryville,Pa., USA) and used as carrier gas for the GC/MS. Parameters for the FIDwith integrating recorder were: threshold, 3; area reject, 100; andattenuation, 2. Parameters for the MS were: mass range, 50 to 550 amu;threshold, 500; scan rate, 1.5 scans/s; and electron multiplier voltage,1600 V according to the automated calibration routine.

The differential mobility spectrometer contained a planar micro-scaledrift tube made from ceramic plates with gold plate copper baseelectrodes. The separating electrodes were 4 mm wide×6 mm long and awidth of 0.52 mm was used for the gap between the electrodes. Electrodeswere fixed in a metal body to which a −1 mCi ⁶³Ni ion source wasattached. The ion source was connected to a transfer line into the GCoven. Air at 0.5 L/min was heated and passed into the transfer line forgas flow through the DMS analyzer. The transfer line and DMS analyzerwere maintained at the same temperature. Air was provided using a pureair generator (Mode 737, Addeo Corp, Miami, Fla.) and was furtherpurified through beds of 13× molecular sieve. Moisture in the carriergas was monitored using a model MIS-2 meter (Panametrics, Inc., Waltham,Mass.) and was 30 ppm or below. The drift tube was operated usingin-house built electronics containing an RF waveform generator, asweeping voltage generator, and an electrometer. The waveform generatorwas based on a soft-switched, semi-resonant circuit that incorporated afly-back transformer and allowed variable peak-to-peak amplitudes of theasymmetric waveform from 200 V to 1600 V without altering the waveformshape. The operating frequency of the RF generator was 1.3 MHz. Acompensation voltage ramp was synchronized with the data collectionsystem and provided a scan of compensation voltage from −10 V (or −5 V)to +30 V (or 24 V) at a frequency of 1 scan every 3.8 (or 2.8) s.Signals were processed using a model 6024E National Instruments (Austin,Tex.) board; spectra were digitized and stored for every scan usingsoftware derived from Labview (National Instruments).

The pyrolysis apparatus was model 150 Pyroprobe (CDS, Inc., Avondale,Pa.) pyrolyzer with a platinum ribbon probe. The probe was housed duringanalysis in a glass chamber, with a gas flow inlet and needled outlet.Dimensions of the glass chamber were: inner diameter, 7.2 mm; outerdiameter, 9.2 mm; and length, 15 cm. The chamber was attached to thepyrolyzer through a ¾″ tube union (Swagelock Company, Solon, Ohio) andthe needle attached to the end of glass chamber via ¼- 1/16″ Swagelokreducing unit. The total volume of the chamber exclusive of the probewas 3.6 mL. Nitrogen was provided to the chamber at 44 mL/min during therun, so the gas volume of the chamber was replaced every 5 s. Thechamber was wrapped with a resistive wire heater and insulated withglass pack to maintain temperature at 250° C. during transfer of thepyrolysate to the GC injection port.

Bacterial Cultures and Growth Condition

Escherichia coli K-12 (strain # 25), Micrococcus luteus (strain # 52)and Bacillus megaterium (strain # 61) were obtained from the New MexicoState University Culture Collection. The three cultures were grown for17 hrs in nutrient broth (Difco, Detroit, Mich.) in an orbital shaker(150 RPM) maintained at 30° C. The cultures were harvested bycentrifugation (10,000 RPM, 2 min.), re-suspended in sterile water, spunagain, and then re-suspended in sterile water. The cells were quantifiedby sequentially diluting the cells and plating sub-samples onto nutrientagar plates, and counting resultant duplicate samples. Under thesegrowth conditions, 66% of the B. megaterium cells had sporulated asmeasured by staining with Brilliant Green and microscopic examination.The cells were pyrolyzed and analyzed on the day of preparation, or werestored at 4° C. and analyzed within one week. Biomarkers included LipidA (CalbiochemNovabiochem Co., La Jolla, Calif.); Lipoteichoic Acid (fromBIOTREND Chemikalien Germany); and dipicolinic acid (Aldrich ChemicalCo, St. Louis, Mo.) and were used as received without further treatment.

Procedures

Several procedures were used throughout the whole of this study andincluded handling and injection of the sample from the pyroprobeapparatus to the GC, data collection using the GC/DMS, data reduction tospreadsheets, and analysis of the data.

Before each measurement, the pyroprobe containing the Pt ribbon washeated to 800-900° C. or inserted into the flame of a Bunsen burner toremove residues of previous measurements. Sample volumes ofapproximately 20 mL were applied by micropipette onto the surface of thePt ribbon and dried at −75° C. in air for 1 to 1.5 minutes. Thetemperature of the glass chamber of the pyroprobe was 250° C.

A 10 μL of bacterial sample was placed on the pyroprobe ribbon. Directlybefore the GC analysis, the pyrolysis apparatus with the pyroprobecontaining bacteria was purged with nitrogen at a gas flow of −44 mL/minfor −6 s (one replacement volume of the pyrolysis chamber). The nitrogenflow was stopped and the needle of the apparatus was inserted throughthe septum of the injection port of the gas chromatograph. Nitrogen wasagain applied to the pyrolysis apparatus and the sample was pyrolyzed at650° C. for 10 s. The gas chromatographic analysis was startedsimultaneously with the start of pyrolysis and the DMS analyzer wasoperated continuously with mobility scans obtained every 2.8 s (cf.above). After 30 s, the pyrolysis gas flow was stopped and the pyroprobewas removed from the injection port. Since the widths of individual GCpeaks were 5 to 7.5 s at the baseline during an elution profile, two tothree differential mobility spectra were recorded for each peak elutedin the chromatogram.

The positive and negative spectra of each py-GC/DMS run were saved asASC 11 files (file size 1.3-1.5 MB). These files were imported intoOrigin 6.1 and plotted into graphs. Quantitative determinations weremade using chromatograms through Peakfit 4.0 (Jandel Scientific, SanRafael, Calif.). Plots of ion intensity versus retention time weredeconvoluted with these PeakFit parameters: for automatic baselinesubtraction, Linear, 2%; peak smoothing, FFT Filtering in levels from 10to 24%; Auto Place and fit peaks, Linear two point baseline; FFT Filter,28 to 54.17 smoothing, options, Chromatography; and Gauss area, 1.5%amplifier.

Results

Profiles from Pyrolysis of Bacteria with GC/DMS

Results from the pyrolysis of three bacteria with GC/DMS analysis areshown as plots of ion intensity, retention time, and compensationvoltage in FIG. 21 and FIG. 22. In FIG. 21, plots for positive ions areshown from the pyrolysis of E. coli, M. luteus, and B. megaterium inframe A, B, and C, respectively. Constituents were seen above backgroundthroughout a column temperature range from 50 to −190° C. (retentiontimes of 0 to 20 min) and between compensation voltages of −2 V to 8 V.The peaks in FIG. 21 arise from reactions (Eq. 1) between substances inthe GC effluent and a reactant ion (H⁺(H₂O)_(n)) seen at a compensationvoltage of −14 V (not shown).

In the differential mobility spectra, the more offset peaks (such as athigher values of compensation voltage) will be of lower molecular weightthan those at 0 V and are consistent with molecular masses of −50 to−120 amu. Peaks with compensation voltages of 0 to −3 V are found withions off high mass which exhibit negative dependence of mobility onelectric field strength (approximately 150 amu and higher). Thus, thecompensation voltage axis can be viewed as a measure of low (at 8 V) tohigh (at −3 V) mass spanning a range from approximately −50 to 250 amu.

Each bacterium produced a pyrolysate with a complex mixture of volatilecompounds and this was observed in results from the GC/DMS, GC/FID andGC/MS. In FIG. 21, a general trend can be seen in the plots forincreases in molecular weight with increases in retention time. However,some differential mobility spectra can be seen with two peaks atdiffering compensation voltages. Commonly in IMS, a protonated monomerwill form a cluster with a sample neutral to form a proton bound dimer,M2H+(H₂O)_(n), when sample vapor concentration is increased. Theproton-bound dimer will appear at the same retention time as theprotonated monomer though compensation voltage will be displaced in thedirection of zero that for the protonated monomer. This can be anadditional component in the orthogonal differential mobility spectrum asa measure of concentration or abundance. An example of this is evidentin FIG. 21C with a component at a retention time of 6 min. where twopeaks are seen at 3.4 V and −1 V in the differential mobility spectrum.These peaks arose from the same substance, crotonic acid, and were theprotonated monomer and proton bound dimer. In the corresponding GC/MSdata set, a single chromatographic peak was observed with the massspectrum of crotonic acid orthogonal to retention time. This can be seenthrough the plots for other substances. The complexity of the plots frompy-GC/DMS is consistent with findings with py-GC/FID and py-GC/MSanalyses made using the same samples under identical conditions ofpyrolysis. The chromatograms could be matched among all threeinstruments within each of the three bacteria samples. The number ofconstituents, resolved and detected, was 50 to 70 using py-GC/FID,py-GC/DMS or py-GC/MS for the total ion chromatograms.

The reproducibility of the py-GC/DMS plots was determined forcompensation voltage, peak intensity and retention time and averagevalues for these were ±0.2 V, 10% relative standard deviation (RSD), and±0.05 min, respectively. The GC/DMS alone with chemical standardsinjected by syringe yielded reproducibility of ±0.1 V, 10% relativestandard deviation (RSD), and ±0.02 min for compensation voltage, peakintensity and retention time, respectively. This demonstrated that thecontribution to variance from sample handling by pyrolysis wasnegligible when compared to the same for a syringe injection, notedabove. Moreover, comparable quantitative variance was obtained frompy-GC/FID analyses suggesting that the DMS as detector was notintroducing significant variance into the analyses versus the FID.Consequently, any differences seen in the patterns of FIG. 21 are notvariability of the DMS but can be associated with chemical differencesof the bacteria as discussed below.

In a micro-fabricated DMS analyzer, vapors ionized in the source regionare swept into the analyzer region where positive and negative ions arepushed through the drift tube and characterized simultaneously. Resultsfor negative ions are shown in FIG. 22 and came from the same data setshown in FIG. 21. The chemistry of ionization is based upon reactionsbetween substances in the GC effluent and negative reactant ions, here,O2 (H20)_(n), which was evident at 11.3 V (off scale in FIG. 22), (seeEq. (2)).

Ionization chemistry with negative ions is generally more selective thanthat for positive ions and based upon O2⁻(H₂O)_(n) attachment to aneutral. This occurs with molecules containing acidic protons orelectronegative groups. In some instances, the product or adduct ion(MO₂ ⁻(H₂O)_(n-1)) may dissociate to form M⁻ or M—H⁻. The plots ofretention time versus compensation voltage for negative ions also showeda large number of constituents between 0 to 20 min elution times andcompensation voltages from 10 to 0 V. However, fewer constituents wereobserved for negative ions versus that for positive ions with from 31 to39 peaks detected and resolved. This is consistent with the anticipatedincrease in selectivity for negative ionization chemistry. Crotonic acidwas noticeable in the negative ion py-GC/DMS plots and was expectedsince carboxylic acids exhibit favorable ionization chemistry with O₂⁻(H₂O)_(n).

The availability of information for negative product ions is anadditional and separate measure of chemical identity over positive ionresponse and is available conveniently with a py-GC/DMS measurement.Such chemical information might be correlated to the response withpositive ion chemistry. Alternatively, the capability for response withnegative ions is an opportunity to employ derivatizing agents that areparticularly well suited for negative ions (fluoro or halo derivatizingagents that have been used with ECDs).

The results in FIG. 21 and FIG. 22 were compared favorably to results bypy-GC/FID and py-GC/MS with the same sample. The results in FIG. 21 andFIG. 22 demonstrate that a DMS analyzer shows response with detail formolecules spanning a range of molecular weights from 50 to 250 amu(gauged from retention time or temperature) and that the existing DMSanalyzer provided resolution of chemical information orthogonal toretention.

Py-GC/DMS Analyses of Biopolymers

Biopolymers for some major constituents in bacteria are available aspurified substances though the choice of materials is limited by genusand species. Lipid A and lipoteichoic acid were obtained commerciallyand were characterized by py-GC/DMS in order to compare theseprospective sources of bacterial chemical information to actual resultsfrom bacteria samples. Studies were made of the biopolymers alone and ofbiopolymers as mixtures with bacteria. Negative controls were made bymixing biopolymers with bacteria missing the biopolymer. Results fromthese studies are shown in part in FIG. 23A to C from py-GC/DMSdeterminations of the Gram-negative bacterium E. coli, Lipid A, and amixture of E. coli with Lipid A, respectively. The findings show thatsome of the peaks from E. coli can be matched to peaks from Lipid Ausing retention time and compensation voltage. However, peaks can beseen in the plot for E. coli which are not associated with and in plotsfrom analysis of Lipid A and peaks can be seen from Lipid A that are notevident in E. coli. The positive control with a mixture showed thatdifferences were not due to matrix effects of any chromatographicuncertainties such as adsorption at active sites. Rather, the profileswere additive as shown in FIG. 23C and the differences cannot beattributed to pyrolysis, GC separation, or ionization chemistry in DMSanalysis. These differences are likely due to the origin and compositionof Lipid A which came from Salmonella minnesota and not from the genusEscherichia. Thus, the patterns seen in the plots for E. coli may beunderstood to arise from pyrolysis of biopolymers other than Lipid A.Results from py-GC/DMS analysis of M. luteus, lipoteichoic acid, and amixture of M. luteus with lipoteichoic acid showed different patternsfrom those in FIG. 23, though the virtually identical conclusions asthat with Lipid A. In this instance, the lipoteichoic acid was isolatedfrom Streptococcus pyrogenes. Consequently, associations between peaksin bacteria with pyrolysis products from biopolymers were unsuccessful.Instead, chemicals known as pyrolysis products from bacteria wereobtained as authentic chemical standards and were used to evaluateresults from py-GC/DMS and py-GC/MS.

GC/DMS Characterization of Authentic Standards for Chemicals fromPyrolysis of Bacteria

Volatile and semi-volatile organic compounds are produced from thepyrolysis of bacteria and these have been recently described by Snyderet al. Samples of most of these chemicals were obtained commercially asauthentic standards and were characterized for retention time (t_(r))and compensation voltage (C_(v)) by GC/DMS, and for retention time andmass spectra by GC/MS. All chemicals except some carboxylic acidsexhibited distinct chromatographic retention, distinctive compensationvoltages, and mass spectra which matched reference spectra (exceptionsincluded carboxylic acids which, apart from a few exceptions, wereeither adsorbed on active sites in the injector port or showed poorchroinatographic efficiency on the non-polar stationary phase). Thelocation of these chemical standards in plots of retention time versuscompensation voltage are shown in FIG. 24 and FIG. 25 with numbersoverlaying points for abundant peaks from py-GC/DMS analysis of E. coli(70 peaks) and M. luteus (50 peaks). Numbers, referenced to the captionin FIG. 24, are placed at the intersection of t_(r) and C, socomparisons can be made, within the error of measurement, betweenauthentic chemical standard values to values of peaks created frompyrolysis.

Results of both chemical standards and two representatives ofGram-positive and Gram-negative bacteria seen in FIG. 24 wherecomparisons shows that not all chemicals reported by Snyder could befound in plots for positive ions. However, 8 of 16 chemicals possiblewere observed as matches in both requirements, i.e., retention time andcompensation voltage, and improvement are expected as chromatographicconditions are optimized. This favorable comparison was confirmed andsupported by GC/MS analysis which demonstrated that the GC/DMS providedchemical information consistent with the reference method (GC/MS) andconsistent with known pyrolysis chemistry described by others. Theresults also demonstrate that more than 75% of the most abundancechemicals in the py-GC/DMS analyses are unknown. The importance of theseother peaks in disclosing chemical information about bacteria is notknown and must be established in further studies.

Matches between authentic chemical standards and py-GC/DMS of bacteria(30 peaks for each bacterium) with negative product ions were alsoevident in a few instances. As seen in FIG. 25, three of the chemicalsgave favorable matches with bacterial plots and the remaining peaks wereof unknown identity. These three chemicals were also the only authenticstandards to give negative ion response. These findings demonstratedthat py-GC/DMS analyses provided some chemical information that shouldbe expected from bacteria.

Discrimination between Bacteria Using Results from py-GC-DMS

The central question in these studies was the suitability for py-GC/DMSto provide analytical information to allow the discrimination betweenbacteria as Gram-negative, Gram-positive, and spore forms. A particularinterest was if useful information was encoded in peaks of strongintensity and hence ease of comparison. Results with spores weredramatic as seen in FIGS. 21 and 22 where a distinguishing andreproducible peak or substance was formed uniquely with spores. Thischemical was identified as crotonic acid using mass spectra, retentiontime and compensation voltage with an authentic standard. Thoughcrotonic acid has not been used previously as a biomarker for spores andis regarded as a chemical for Gram-positive bacteria in general,crotonic acid was not seen above detectable levels in analyses bypy-GC/MS or py-GC/DMS of M. luteus. Rather, B. megaterium with highspore content only produced crotonic acid here. In prior studies, sporeswere distinguished by the presence of picolinic acid and pyridine ormethyl derivatives of picolinic acid. Unfortunately, picolinic acid wasabsorbed on active sites of the injection port when solutions of 10-100ng/μl were analyzed. Discrimination between Gram-negative andGram-positive bacteria required detailed attention to plots in FIG. 24and FIG. 25 and the identification of peaks unique to each bacteriumtype.

Of the 70 peaks seen in FIG. 24 from E. coli, the majority were found inlocations of retention time and compensation voltage distinct from M.luteus. Which of these peaks might be useful, alone or in combination,as biomarkers for Gram-negative bacteria and which will be too dependentupon cell history to be analytically useful has not been determined. Thelarge number and separation for other peaks is promising. Less promisingis the distinctiveness of analytical data for Gram-positiverepresentative, M. luteus. Few intense peaks were observed for py-GC/DMSanalysis of M. luteus and most of these are coincident with peaks fromE. coli as seen in FIG. 24. Only four peaks in the presentinstrumentation and pyrolysis methods can be distinguished fromGrain-negative bacteria and these are seen at retention times of 5, 5.2and 13.5 min. However, the unpromising condition is substantiallyaltered with chemical information is introduced from negative ions.Plots for negative ions are shown in FIG. 25 and provide anotherdimension of chemical information (t_(r), C_(n) and ion polarity) and inthis instance, nearly nine peaks were observed for Gram-positive M.luteus and were thought to be characteristic markers for M. luteus.These are seen at retention times (min) of 2, 3.6, 4, 6.5, 9.5, 11, and12.5. This demonstrates an advantage of DMS over traditional IMS withthe simultaneous characterization of positive and negative ions.

Resolution and Sensitivity with Separation Field and Temperature of theDMS Analyzer

In one practice of the invention, the separation voltage was varied toexplore effect on resolution between peaks on the compensation voltageaxis. Results are shown in FIG. 26 from py-GC/DMS characterization of B.megaterium for positive ions from four settings of the separationvoltage (low to high, bottom to top). In FIG. 26D, the reactant ion peak(Equation 1) is evident at compensation voltages from 3 V to 5 V with acenter at 4 V. Throughout this analysis, this peak is visible andexhibits a small drift in compensation voltage. This is attributed to asmall increase in temperature of the drift tube during the GC columntemperature program caused by poor thermal control of the drift tube. Atlow separation voltage, product ions appear throughout the chromatogramat compensation voltages between 2.5 to 0 V, a small band fordistribution of analytical information. As voltage is increased from 688V to 860 V (FIG. 26C), the reactant ion peak is shifted from −4 V to−7.5 V consistent with a positive alpha function known for hydratedprotons. Product ions in positive polarity also show changes incompensation voltage as the separation field is increased and some ionshave been shifted to compensation voltages higher than those in FIG.26A. These are known to occur through changes in AK and arecharacteristic of ions with masses below 150-200 amu, namely protonatedmonomers of small molecules as marked in FIG. 26. Other peaks wereshifted toward a zero or negative voltage as the separation voltage isincreased and such ions have negative dependence of mobility on electricfield. In prior studies, these ions exhibited masses larger than 250 amuand have been associated with proton bound dimers. Thus, the presence oftwo peaks of differing compensation voltage at the same retention timecan arise from distribution of charge between protonated monomer andproton bound dimer as governed by vapor concentration as found inconventional mobility spectrometers. The advantage of this is thatconcentration information is available directed in the differentialmobility spectra and the range of separation voltages allows control ofresolution within boundaries.

Further increases in separation voltage to 944 V (FIG. 26B) and to 1032V (FIG. 26A) lead to exaggeration of the patterns seen in FIG. 26D andFIG. 26C. The reactant ion peak is displaced to 14 V and a dramaticdecrease in peak intensity was observed. This loss in intensity isobserved in general with this DMS design and the cause is not fullydescribed. A similar shift in compensation voltage and loss in peakintensity is also evident with product ions. The shift in compensationvoltage means that resolution within the differential mobility spectraincreases considerably with each increase in separation voltage; this isexpected from plots of mobility dependence with electric field.Nonetheless, a compromise between resolution and peak intensity wasfound at 944 V and was used throughout all the studies presented above.

Measurements for negative ions paralleled the trends seen with positiveions. Product ions were seen between −4 to 2 V at low separation voltageand resolution of peaks improved on the compensation voltage axis as theseparation field was increased. Unlike positive ions, negative ionclusters such as M₂O₂ ⁻ are not commonly observed at these vapor levelsand the pattern with increased separation voltage was comparativelysimple with single ions for each chromatographic peak. Nonetheless,product ions were shifted toward greater AK and larger compensationvoltages with increased separation voltage. Loss in peak abundance wasobserved also with negative ions with greatest loss occurring between944 and 1032 V, consistent with the product ion behavior.

Detectors in gas chromatography are operated generally at temperatures50° C. or higher above the maximum temperature applied to the column andthese guidelines are intended to prevent sample condensation in thedetector. However, temperature has secondary effects in IMS analyzersincluding ion declustering, dissociation, or decomposition. Thus, aconcern was the compromise between sample condensation in the detectorand distortion of analytical information through changes in ionstability with temperature increases. Results from py-GC/DMS screeningof B. megaterium with four temperatures of the DMS drift tube are shownin FIG. 27; gas temperature was determined in the flow vented from thedrift tube. The pattern of peaks at two or more compensation voltagesseen at 55° C. (FIG. 27D) are characteristic of the presence ofprotonated monomers and proton-bound dimers routinely observed inmobility spectrometers including DMS at low temperatures. An example ofthis is the pattern at 6 min. where peaks appear at compensationvoltages of 3.5 V and 0 V for protonated monomer and proton bound dimer,respectively. However, as temperature is increased in steps, intensityfor the peak of the proton bound dimer declines and is missing at 115°C. (FIG. 27A). Though a slight decline in intensity for all peaks wasobserved with this temperature change, the peaks at compensationvoltages of I to −1 V, understood to be cluster ions, were lost from theDMS scans uniformly at all retention times.

Though decreases in temperature may be expected to alter thechromatographic pattern through losses of sample by condensation forsubstances that elute at high column temperatures, there is no apparentloss of chromatographic detail above retention times of 10 min (115° C.)or 15 min (150° C.) when the DMS is low temperature of 55° C. Attemperatures up to 110° C., there was no observable increase in numberof peaks eluted from the column though apparent sensitivity of the DMSdecreased with increased temperature. After some weeks of py-GC/DMSmeasurements with the DMS at 55° C., decreased intensity in response wasobserved uniformly for all substances throughout the retention timescale and was attributed to a gradual accumulation of sample ascondensate in the drift tube. This diminished response was reversed byheating the drift tube to 110° C. or higher; heating was accompanied byloss of reactant ion peaks which were replaced by a single peak near 0V. This was understood as excessive vapor levels of the source regionproduced from off gassing of condensed sample in the source region.After some hours the analyzer was restored in clean response as seen inthe differential mobility spectrum.

Comparable trends noted above for B. megaterium in resolution, spectralprofiles and contamination at various temperatures were obtained alsofor E. coli and M. luteus. A temperature for the DMS was a compromisebetween eventual loss of response at low temperature throughaccumulation or condensation of impurities and the loss of detail indifferential mobility spectra from ion declustering at high temperature.A temperature of −90° C. was chosen in further studies and provided abalance between stable sensitivity over long periods and differentialmobility spectra with multiple peaks or bands.

Quantitative Py-GC/DMS of Bacteria

Mobility spectrometers equipped with radioactive ionization sources suchas ⁶³Ni exhibit proportional and quantitative response toward vaporconcentrations for peak intensities in mobility spectra though linearranges may be only 10-100. Differential mobility spectrometers showdetection limits from 10-100 pg for volatile organic compounds andlinear ranges of 100-1000. Response from py-GC/DMS analysis of bacteriais shown in FIG. 28 for integrated peak area versus number of bacteriaapplied to the pyrolysis probe. The plots were made using only the areafor a single biomarker and the DMS was operated for maximum ionresolution (a large separation voltage). Consequently, the plots in FIG.28 do not represent optimum conditions of temperature, separation field,or data processing to establish a limit of detection. Rather, thesestudies were made to establish if a quantitative basis existed betweenthe pyrolysis step and the observed response. The plots suggest that thesum of all parts of the measurement including pyrolysis and DMS analysisare linear in the range explored. No additional efforts were given toprocessing the data through sum of all product ion intensity.Presumably, additional dynamic range or improved detection limit shouldbe possible if the signal was processed and integrated or if onlyseveral biomarkers were integrated and summed.

The minimum number of bacteria seen in this early studies was 10°bacteria where each bacteria showed characteristic response where n forbacteria were 4.6, B. megaterium; 5.8, M. luteus, and 6.8 E. coli. Thedetection limits will be governed by the DMS through the balance betweenresolution and ion yield, which are inversely related and controlledprimarily by separation field. That is, increased resolution attainedthrough increased separation field results in this generation of DMSwith increased ion losses. In limited studies to confirm theseexpectations, separation fields were decreased and 6000 bacteria weredetected for E. coli using a single biomarker.

Example 8 Comparison of IMS-TOF to DMS: Resolution of Meta- and ParaXylenes

To illustrate the advantages of the method and apparatus of theinvention, compounds that are extremely difficult to resolve intime-of-flight ion mobility spectrometry (TOF-IMS) are shown to beeasily resolved in DMS practices of the invention herein. TOF-IMS is ahighly sensitive, quantitative method for organic compound detection. Ithas been used for detection of chemical warfare agents, illicit drugsand explosives, and unlike mass spectrometry, it operates like thepresent invention at atmospheric pressure, eliminating the need forvacuum tight seals and power consuming vacuum pumps.

However, the TOF-IMS operates with low strength electric fields wherethe mobility of an ion is essentially constant with electric fieldstrength, while the present invention operates in periodic high fieldsand filters based on the non-linear mobility dependence of ions on thehigh strength fields. Thus the invention can provide more and differentstructural information about ion species that further enables accuratespecies detection and identification. Further comparison with TOF-IMS isinstructive.

It will be understood that mixed xylenes are the second-most-importantaromatic product for chemical manufacturing around the world, rankingbehind benzene and ahead of toluene. Of the three isomers (ortho-, meta-and para-xylene) p-xylene is the most widely used isomer in themanufacture of polymeric materials. Separation of these isomers isgenerally challenging with most analytical instruments. Since theseisomers have the same molecular weight they cannot be resolved in a massspectrometer.

In conventional TOF-IMS these compounds have virtually overlappingpeaks, as shown in FIG. 29. While these compounds can be resolved in agas chromatograph (GC), this typically takes more than 20 minutes.Meanwhile devices in practice of the invention enable excellentresolution of the para and meta xylenes in under one second. FIG. 30shows these compounds clearly resolved in practice of the invention,notwithstanding such surprisingly rapid performance.

Example 9 High Sensitivity of DMS in Detection of Methyl Salicilate

FIGS. 31 and 32 show the response and concentration dependence in DMSpractice of the invention for methyl salycilate, a chemical warfareagent simulant. FIG. 31 shows positive ion spectra for differentconcentrations of methyl salycilate. FIG. 32 shows concentrationdependence of the system to methyl salycilate for both positive andnegative ions. Samples with concentrations of methyl salycilate down toabout 45 parts-per-trillion are readily detectable in this device. Themethyl salycilate compound produces both positively and negativelycharged ions which exhibit similar concentration dependences. Theapparatus of the invention is able to simultaneously detect both ionresponses within the same analytical run. Producing simultaneouspositive and negative ion species information improves compoundidentification at reduced detection times.

Example 10 Smoke Analysis from the Combustion of Cotton, Paper, Grass,Tobacco and Gasoline Samples using GC-DMS

Materials and Methods

Smoke from combustion of cotton, paper, grass, tobacco and gasoline (inan internal combustion engine) were sampled by SPME and the samples werescreened using a GC-DMS. As a control, a measure of the chemical vaporcomposition of several materials using GC-MS was performed, as well asdiscrimination of vapor profiles between the tested analytes (includingseveral cellulose materials) by GC-DMS, and then identification ofchemical markers specific to the burning of a particular material.

In one demonstration of the invention, model 5880 gas chromatograph(Hewlett-Packard Co., Avondale Pa.) was equipped with a HP splitlessinjector, 25 m SP 2300 capillary column (Supelco, Bellefonte, Pa.), aflame ionization detector, and a DMS detector. A model 5880 gaschromatograph (GC) (Hewlett-Packard Co., Avondale Pa.) was equipped witha HP splitless injector, 25 m SP 2300 capillary column (Supelco,Bellefonte, Pa.), a flame ionization detector.

The carrier gas was nitrogen (99.99%) scrubbed over a molecular sievebed and pressure on the splitless injector was 10 psig with a splitratio was 50:1. Other experimental parameters for the GC included:initial temperature, 30° C.; initial time, 5 min; program rate 15° C.minI; final temperature, 200° C.; final time, 1 min.

The DMS detector was equipped with ˜0.6-1 mCi of 63Ni. The drift gas wasair at 1 to 21 min-1 from a model 737 Addco Pure Air generator (Miami,Fla.). The drift gas was further purified over a 5 Å molecular sieve bed(10 cm diameter×0.6 m long) and passed through heated stainless steeltubing to warm the drift tube to 70° C.

The analytical column was attached to the DMS drift tube through a 30 cmlength of aluminum-clad column and column effluent was carried by driftgas through the ion source region for sample ionization. The drift gasalso carried product ions through the gap (0.5 mm) between two flatseparating electrodes (5×25 mm). Two electric fields were applied to thedrift tube: a non symmetric waveform high frequency (1.3 MHz) withstrong electric field (20 kV cm-1 peak to peak amplitude) and a weak DCfield (−360 V cm-1 to +80 V cm-1) of compensation voltage (−18 to +4V).Signal was processed using a National Instruments board (Model 6024E),digitized and stored. Excel 97 (Microsoft Corp) and Origin v 5.0 wereused to display the results as spectra in topographic plots and graphsof ion intensity versus time.

The gas chromatograph-mass spectrometer was a model 5890 A gaschromatograph and Model 5971A mass selective detector (Hewlett-PackardCo., Palo Alto, Calif.) and was equipped with a 25 m SP 2300 capillarycolumn (Supelco, Bellefonte, Pa.). The operating parameters of the gaschromatograph/mass spectrometer (GC/MS) were identical to those forGC-DMS listed above. Conditions for the mass spectrometer were: massrange, 45-550 amu; threshold, 500; scan rate, ˜200 amu s-1; and electronmultiplier voltage, 2100-2500 according to the automated calibrationroutine.

Solid phase micro-extraction (SPME) fibers and injector were obtainedfrom Supelco (Bellefonte, Pa.). A mixture of hydrocarbons (hexane tohexadecane) was prepared in methlyene chloride solvent at 100 ng/ul peralkane. The alkanes were obtained from various manufacturers and wereused as a standard for calibration of chromatographic retention.Materials were all obtained locally and included paper as shreddednewspaper; cotton; tobacco as cigarettes; and grass as dried Bermudagrass.

Procedure

In one demonstration, a wad of ˜9 cm3 of loosely held material(cigarette excepted) was placed in the end of a borosilicate glass tube(2.54 cm OD×6 cm long) which was held level and a flame from a butanelighter was used to ignite the sample. The apparatus was placed in afume hood where flow of air created air flow through the tube andallowed a sustained but low level burn of the sample over 3-8 minutes.Hot vapor and particulate emissions from the sample were released in aplume from the sample and the SPME fiber was held in this plumesimulating field sampling of ambient air.

The time of sampling was 4 s for cotton, 6 s for cigarettes, 8 s forpaper and 10 s for grass. Samples of engine exhaust from a forklifttruck were taken by holding the SPME fiber in the exhaust streamapproximately 0.5 meter from the end of the tailpipe. The samples werefreshly analyzed by GC-MS or GC-DMS. In an injection, the SPME wasplaced in the injection port under splitless mode and held for 30seconds until the inlet was switched to split mode. The SPME fibers wereconditioned between runs for 10 minutes at 220° C. in nitrogen.Repeatability was obtained by four replicate measurements of cottonburns with 4s sampling of the smoke plumes. The alkane standard was usedto calibrate retention on the GC-MS and the GC-DMS.

Detection of VOC from Combustion of Fuel Sources by GC-MS

A preliminary requirement in this study was to determine if smokesamples taken by SPME methods and analyzed by capillary GC-MS wouldprovide chromatographic profiles for VOCs sufficiently distinct to beattributed to specific fuel sources. Results from GC-MS analysis of SPMEsamples from four of the five combustion sources (cotton, paper, grassand engine exhaust) are shown in FIG. 33 as total ion chromatograms.These VOCs spanned the range of carbon numbers from 10 to 18 as shown inretention times for the alkane standard under identical conditions. Time(in minutes) for the alkanes (not shown) were: decane, 4.27; undecane,5.54; dodecane, 7.00; tridecane, 8.40; tetradecane, 9.81; pentadecane,11.17; hexadecane, 12.47, and octradecane, 15.79 (alkanes with carbonnumbers below 10 were lost in the solvent delay). The traces in FIG. 33spanning 2 to 20 minutes retention illustrate that all samples exhibiteda complex mixture of VOCs from adsorbed aerosols (desorbed in theinjection port) and molecular weights for these compounds can beestimated as 150 to 250 amu. Additional chemical information forcompounds with molar masses below 150 amu was not sought as suchcompounds were regarded as too volatile to be collected by SPME samplingmethods. Also, no particular effort was made to measure constituentsabove 250 amu. The emphasis in these measurements was a comparison ofemission composition available by SPME sampling without requirements forcryogenic options or ultra high temperatures. Thus, these findings arenot a comprehensive chemical characterization of vapors and themeasurements were made in anticipation of practical, field-portableinstruments which would be engineered for operation under simpleconditions according to embodiments of the invention.

In the range of molecular weights screened in FIG. 33, clear differencesexisted in the qualitative and quantitative distributions of peaks inthe chromatographic profiles. While the profiles of total ionchromatograms appear distinctive in FIG. 33, peaks in cotton, paper andgrass were shared in common by these cellulose based materials thoughdifferences could be found in relative abundances. An inspection of thechromatograms showed that there were 10 constituents in cotton that weredistinctive over all other constituents in other samples and thesedistinctive components are shown in Table 1. In summary, these findingsdemonstrated that the chemical composition of emissions from burningmaterials of interest exhibited measurable chemical differences throughanalysis by high resolution GC-MS. Thus, there is a chemical basis foran advanced smoke detector to discriminate between source materials offires. Naturally, exhaustive studies on the composition of smoke andreproducibility of sampling and analysis would be needed to furtherrefine these observations. However, precision (discussed below)demonstrated that the differences were not random, encouraging furtherstudy.

Ion mobility spectrometers are equipped with an atmospheric pressurechemical ionization (APCI) source and an intermediate step was todetermine if the pre-separation could be eliminated from the method.Direct sampling of emissions using an APCI mass spectrometer was made todetermine the APCI response to effluent constituents and to measure theresolution possible with a mass spectrometer alone.

The mass spectra from direct sampling of vapors with a corona dischargeion source for grass, cotton and cigarettes are shown for positive ionsin FIG. 34 and Table 2. In the background air, the reactant ions wereions with m/z 19, 35, 55, 73 amu corresponding to ions of H3O+(H2O)nwith n=0, 1, 2, 3, respectively. Distinctive among these spectra fordirect sampling of combustion emissions is that for cigarette smokewhere nicotine is evident at m/z 163 amu. Nicotine has a large protonaffinity and has been known for decades to yield protonated monomersthrough reactions as shown in Equation 3:

Consequently, nicotine preferentially acquired charge from the reactantions over other sample vapors and became the dominant ion throughcompetitive charge exchange. Other constituents are present (as shown inFIG. 34, cigarette smoke) but the nicotine protonated monomer towersabove all other peaks in the APCI mass spectrum.

In the other samples, the distribution of vapor concentrations andproton affinities of the VOCs yielded complex mass spectra with massesbetween 60-200 amu for grass and cotton. There were complex with ionscommon to each owing to gas phase ionization reactions at ambientpressure. Though multivariate methods might be employed to categorizethe sources responsible for the mass spectra in FIG. 34 (cotton smokeand grass smoke), the peaks were separated by unit mass generally in themass spectrometer (Table 2). The resolution of a mobility spectrometeris inadequate to provide satisfactory separation of such complex ionmixtures. Therefore, pre-separation, such as by capillary GC, wasregarded as essential for highly reliable separation and identification.

GC-DMS Analysis of VOC from Combustion of Various Materials

While samples may be drawn directly from the ambient environment intothe first separation stage S-A in embodiments of the invention, we nowdiscuss GC-DMS analysis of SPME-collected samples of combustionemissions, as shown in FIGS. 35 and 36 as chromatograms of totalintensity of product ions from the mobility scans in comparable formatto total ion chromatograms from GC-MS (see FIG. 33). Plots are shown forcotton, paper grass, cigarette and gasoline engine smoke and thefindings reflect the same level of complexity (i.e., number of resolvedconstituents) as seen above in the GC-MS plots. Here also, as expected,the VOCs spanned the range of carbon numbers from 10 to 18 as shown inretention times spanning 3 to 15 minutes. For the alkane standard (notshown) under identical conditions times (in minutes) were: nonane, 3.54;decane, 4.52; undecane, 5.81; dodecane, 7.24; tridecane, 8.77;Tetradecane, 10.27; pentadecane, 11.78; and hexadecane, 13.43. The runwas ended before octadecane eluted; alkanes with carbon numbers belownine appeared in a large unresolved peak from 2 to 3.5 minutes.

Differences were observed in relative abundances of constituents withinthe chromatograms between FIG. 34 and those in FIGS. 35 and 36. This isassociated with differences in response factors between massspectrometry and ion mobility spectrometry or differences between vacuumbased ion formation and ionization at atmospheric pressure. In thelater, response is roughly approximated by proton affinities ofmolecules. Thus, what appear as minor constituents in emissions fromcotton between 8 to 10 minutes (FIG. 33) appear as significantconstituents at the same retention time in FIG. 35. On the one hand,cigarette smoke nicotine dominated the DMS chromatographic response(FIG. 36) as it did the MS trace (FIG. 34). On the other hand, theresponse to small molecules from C10 to C14 by DMS (FIG. 36) was clearlymore pronounced than that from MS (FIG. 34).

Reproducibility was determined using the peak heights on the product ionplots of FIGS. 35 and 36 and results are shown in Table 3 for severalpeaks from throughout the elution program. The relative standarddeviation of the measurement was ranged across a comparatively narrowgap from 17 to 30% RSD. This variation included all aspects of samplepreparation, sampling, measurement, and automated data reduction. As aconsequence, results from this method exhibited actual differences thatcould not be attributed to variance or random error even though samplingwas made with comparatively casual attention to the limitations of SPME.

The peaks unique to cotton were labeled in FIGS. 33 and 35 and summariesof the mass spectral properties for these are shown in Table 1. TheGC-DMS results could be compared directly to the findings from GC-MS andcertain peaks were found in the cotton to be unique or special to cottoncombustion. These are labeled in FIG. 35 and mass spectral propertiesare listed in Table 2. The 2D plots are particularly good forquantitative measures but do not disclose the analytical value oforthogonal information available in the mobility scan. This can be seenin the topographic plots of FIGS. 37 and 38.

Topographic plots from GC-DMS analysis of all samples demonstrated thatinformation in the mobility scan provides distinctiveness for eachsample. The most distinctive of the plots, shown in FIGS. 37 and 38, isthat from the internal combustion engine where incompletely combustedhydrocarbons appear in a narrow band of compensation voltage from −2 to2 V. This was consistent with mass spectra and with the alkane standardwith peaks of similar compensation voltage. Plots for the cellulosematerials (cotton, paper, and grass) exhibited some common features withpeaks from 5 to 14 minutes evenly distributed and compensation voltagesthat spanned −10 to +5V. In general, the compensation voltage trendedfrom −10V toward 0V with increased retention time. These results werepromising as an examination of the concept of GC-DMS as an advancedsmoke detector. As well, it is further noted that cotton exhibitedunique or characteristic peaks in the 3-D plots as labeled in FIG. 37(cotton) and FIG. 33 (cotton).

All of these results had been obtained using comparatively slow GCtemperature ramps. The 15 minutes might be reduced substantially with afast GC. An essential question is what information is available in theplots and to what degree can this information be compressed withoutlosing measurement resolution beyond a usable condition. In massspectrometry, selected ion monitoring is used to improve detectionlimits and can add selectivity through ion ratio measurements. This sameconcept can be applied to DMS to monitor certain ions. This approach tomeasurement provided a reliable route to fast chromatography (FIGS. 39and 40).

In FIGS. 39 and 40, plots of ion intensity at four compensation voltages(4.06V, −1.8V, −4.47V, and −10.35V) are shown top to bottom in eachframe for cotton, paper, grass and gasoline engine exhaust. With thisapproach which is analogous to ion chromatograms in GC/MS measurements,certain regions of compensation voltage were graphically extracted fromthe matrix of retention time, compensation voltage and ion intensity. Ameasure of the amount of chemical information in the selected ionmobility plots from GC-DMS can be seen in these figures wheredifferences in samples are further accentuated. These patterns aredistinct and show that selected ion plots allow a route to chemicalidentification where information can be compressed through fastchromatography. A further embodiment includes forming ratios of two ormore extracted ion chromatograms.

The findings in FIGS. 39 and 40 demonstrate that adequate resolution ofpeaks is available in these complex patterns to compress thechromatographic time scale. At present the scan time of 1 s may be tooslow for below 3 minutes. Since ion residence in the drift tube is 1-2ms, ion hopping could occur for a set of ions in 40 ms, (4 ions for 10ms each). Thus, high speed GC where the complete separation occurs in 60seconds is preferred to allow high cycles (e.g., 1000) throughout themeasurement. The time resolution of 1 part in 1500 would be comparableto the current value of 1 in 960. Thus, should all other facets ofseparation be scalable, the drift tube with ion hoping enables highspeed GC-DMS as a realistic smoke detector to distinguish sources ofsmoke.

TABLE 1 Retention times and ions in mass spectra from peaks that appeardistinctive to cotton emissions. Peak Retention Time Prominent Ions inorder of abundance No* (min) (base peak abundance) 1 5.51 43 (190,000)72, 55, 83, 98 2 7.13 42 (180,000), 41, 55, 86, 96 3 9.09 55 (24,000),126, 41, 42, 43, 53, 69 4 9.55 42 (42,000), 41, 57, 56, 100 5 9.94 43(19,500), 41, 55, 57, 70, 69, 83 6 10.19 44 (390,000), 57, 43, 41, 128 711.78 69 (110,000), 57, 41, 42, 70, 43, 144 8 12.61 102 (54,000), 132,101, 78, 77, 51, 50 *Refer to FIG. 33.

TABLE 2 Ion masses from direct sampling of smoke from cigarettes, grass,and cotton with analysis by atmospheric pressure ionization massspectrometry Cigarettes Grass Cotton Mass Intensity Intensity Intensity37 10,064,000 5,420,000 44 1,210,000 55 6,562,000 4,558,000 60 1,070,0004,050,000 6,978,000 70 732,000 71 1,290,000 73 1,054,000 74 866,000 751,812,000 80 1,020,000 2,532,000 81 1,010,000 83 1,546,000 1,340,000 855,398,000 1,276,000 87 3,416,000 88 728,000 90 782,000 94 2,144,0001,528,000 97 5,890,000 5,960,000 99 3,986,000 1,630,000 101 2,104,000102 2,020,000 103 3,338,000 104 1,102,000 106 1,134,000 108 930,000 1091,548,000 111 2,874,000 6,284,000 113 2,010,000 2,042,000 115 2,860,000116 1,558,000 117 2,960,000 118 996,000 123 2,244,000 125 3,160,000 1271,694,000 1,912,000 129 1,068,000 130 990,000 137 1,430,000 1391,424,000 142 866,000 164 7,034,000

TABLE 3 Reproducibility of combustion experiments including sampling,GC-MS determination and data reduction. Measurements were made using 4 sburns of cotton with four complete replicate experiments. Retention TimeStandard % Relative Standard (min) Area Deviation Deviation (% RSD) 2.920696587 5188474 25.07 5 26439681 5973165 22.59 8 19698838 6011899 30.5211.8 12360466 3020822 24.44 12.7 10095391 1749393 17.33 14.02 38733341167082 30.13

Example 11 Detection of Chemical Warfare Agent Stimulants

With the continuing threat from chemical and biological weapons, theneed for more effective and reliable detectors continues to be an issuefor both the military and homeland security. Most, if not all, oftoday's deployed detection devices were developed to address therelatively narrow range of classic warfare agents (CWAs) of the cold warera. However, with the escalation of world terrorism there comes theneed to deal with a broader range of threats that include a substantiallist of toxics, including so-called toxic industrial chemicals and toxicindustrial materials (a.k.a. TICs and TIMs). This places an even greaterburden on detector technologies which must offer even higher selectivitywithout compromising sensitivity. The requirement is for fast responsetimes with significantly lower false positives. Most of the currentlydeployed detectors are based on IMS technology, developed to maturityover the last several decades and now struggling to adapt to theseincreasing/changing requirements. Meanwhile, practices of the presentinvention overcome these difficulties.

There are a variety of different interferences present in real worldconditions such as: Aqueous Fire Fighting Foam (AFFF), diesel fuel,gasoline, pesticides, paints and floor waxes that lead to a high rate offalse positives in the currently deployed conventional IMS detectors.Frequent false alarms are often experienced in the dusty, smoke-ridden,environments. These lead to a loss of confidence in detection equipment.These false positives can be caused in IMS equipment by the fact thatmany ion species can have the same, or very similar, low field mobilitycoefficients. Practices of the present invention overcome thesedifficulties as well.

In one practice of the invention, trace compounds were detected afterionization with a ⁶³Ni radioactive source. To demonstrate the invention,experiments were performed with calibrated standards of the CWAsimulants: Dimethyl methylphosphonate (DMMP),Diisopropylmethylphosphonate (DIMP) and Methyl Salicylate (MS). Threeindependent vapor generator systems (Vici Metronics Inc, Model 190) wereused to generate controlled air mixtures of the simulants at differentconcentrations. Permeation sources were purchased from KIN-TEK withcalibrated emission rates of 160 ng/min DMMP at T=80 C, 301 ng/min DIMPat 100 C, and 5240 ng/min MS at 100 C. Gas flow rates in all threesystems were the same 100 cc/min. The maximum sample concentrations thatcould be provided was 1.6 mg/m³ for DMMP, 3.01 mg/m³ for DIMP, and 52.4mg/m³ for MS.

The DMS filter was operated in one aspect where it sampled effectively100% of an incoming trace gas sample. In a 100% duty cycle aspect of theinvention, the compensation voltage is fixed such that a particular ionspecies, identified by its differential mobility, is permitted to reachthe detector. This is in contrast to conventional IMS which typicallyuses a gate which is pulsed “open” for approximately 1% of a measurementcycle resulting in only about 1% of the ions being sampled. The DMSfilter of this embodiment did not contain an ion-gate as in IMS devices,and is therefore more sensitive than gated approaches (where largeportions of the sample signal are discarded). In addition to the absenceof a gate, in the present invention it is possible to improvesensitivity wherein the signal can be integrated over a relatively longperiod of time.

The DMS was also operated in a second aspect in order to produce aspectroscopic output by scanning a range of compensation voltages. Thisreduces the “effective” duty cycle, but since the range of compensationvoltages that is scanned can be selected by the operator, the“effective” duty cycle for any type of ion species is significantlyhigher than in conventional IMS. The sensitivity of the system is higherthan conventional IMS with the ability to detect compounds in the pptrange.

Increased sensitivity is invaluable, especially in applicationsrequiring miosis level detection. However, a detector which has highsensitivity without selectivity leads to an even higher rate of unwantedfalse positives. As previously mentioned, enhanced selectivity in theDMS systems of the invention are provided by changing the electric fieldstrength applied to the ionized molecules. In practice, this translatesto changing the field strength of the asymmetric oscillating RF field(Vrf). Changing the RF field results in a corresponding shift in thespectral peak position, as measured by the compensation voltage.Changing the RF field leads to tunable resolution accessed by changingthe RF filtering amplitude and thus changing the operating point on themobility vs. electric field curve. In the system the various RF fieldvalues can all generated under the automatic control of themicroprocessor. The tunable resolution makes it possible to separatemonomers from dimers and other clusters and to use these cluster peaksto aid in the identification of compounds, for example, at FIG. 41 (topcurves).

Tunable resolution also enables the RIP (reactant ion peak) to bedisplaced away from the peaks of interest. The RIP is a background peakthat frequently interferes with the detection of targeted compounds inconventional IMS. This property of the invention enables the detectionof trace compounds in backgrounds that produce interfering signals, orin some situations where the RIP or other compounds would otherwiseinterfere with successful detection. Tracking how the spectral peakposition shifts with RF field provides a great deal of informationunique to that ion species, peaks for other ion species will shift verydifferently. These are species-specific signatures which can be used toidentify detected species in practice of the invention. As earlierdescribed, embodiments of the present invention can simultaneouslydetect both positive and negative ion peaks, modes, which further helpsto improve selectivity. The absence or the presence of peaks, and theirsize and location, in the positive ion channel versus the negativechannel provides more information on the specific compound identity. Theratios between intensities of positive ions and negative ions for agiven sample also provides additional information which enhancesconfidence of the detection.

FIG. 42A and FIG. 42B illustrate this for the nerve agent GA. Thesespectral plots were measured at a Vrf of 1,482 v which corresponds to afield strength of 29,640 v/cm. The characteristic spectrum for thepositive ions is very different from the negative ion spectrum.

The combination of the positive and negative ion channel information,together with the information provided by monitoring the spectral peakshifts as a function of the applied RF field, results in a powerful toolfor chemical identification in practice of the present invention.

In some cases it is desired to achieve narrower peaks and better peakresolution, such as for discriminating between peaks for similar orinterfering analytes in a sample. An additional embodiment of thepresent invention addresses this concern by operating the system atslightly reduced pressures relative to atmosphere. Under these reducedpressure conditions, down to 0.5 atmospheres, the resolution accordingto the invention is significantly increased.

The effect of reduced pressure is illustrated in FIG. 43 for three CWAsimulants, DMMP, DIMP, and MS. The top spectra show the results obtainedat atmospheric pressure, RF=1000V, while the next spectra was obtainedat 0.65 atm, RF=800V, and the bottom spectra was obtained at 0.5 atm,RF=650V. It will be appreciated that the top scan discriminates betweenthe three simulants with some spectral overlapping but which may beadequate in some cases. However the next lower scan has betterresolution (narrower peaks) and the lowest scan has even betterresolution. Thus it is possible to discriminate between such analytes ina sample by reducing operating pressure, according to aspects of theinvention.

A further advantage of reducing pressure in the system is that theamplitude of RF voltages required to filter the ions can be reduced,this results in a lower power requirements which is especially importantfor field-portable systems of the invention.

In one embodiment of the invention, direct sampling of volatile chemicalagents provides adequate detection results, as was the case with FIG.41, especially in the upper scans. However it is also possible to use afirst stage of separation, such as previously discussed which results inproviding a less complex ionized sample to the DMS, resulting in a lesscomplex sample being ionized and filtered in the DMS filter.

In one practice of the invention, a membrane was used at the input ofthe DMS filter system prior to ionization, such as at separation stageS-A in FIG. 2A. The plots of FIG. 43 were obtained with such a membranefront end. Selection of membrane is guided by the need to selectivelypass CWA agent molecules while acting as a barrier to moisture andheavier molecules (whether dirt, dust, hydrocarbon exhausts or thelike). Thus a better and more controlled analytical environment can beprovided within a detection system of the invention with a less complexsample being ionized and filtered within the DMS filter. The plots ofFIG. 43 were taken using a membrane front end as separator thatselectively introduced the detected CWA agents as indicated while actingas a barrier to moisture and unwanted heavier molecules. Variousmembrane materials are known in the art, including partially porousmaterials. These materials may include Teflon, latex, pdms, dimethylsilicone, or the like, as may be used in membrane practices of theinvention.

One of the critical aspects of a CWA detector is how well it can rejectinterferants to prevent false alarms. One particular interferant,Aqueous Fire Fighting Foam (AFFF), has proved extremely challenging forconventional IMS to resolve from CWAs, or CWA simulants. The AFFF peaktends to overlap with that of the agent peak in IMS. FIG. 44demonstrates a practice of the invention for a series of warfare agentsimulants selectively mixed with 1% headspace of AFFF. As can be seen,good DMS peak resolution can be achieved in practice of the invention.There are eight spectral plots in FIG. 44. The top plot shows the RIPfor a DMS system with background air but no sample present with thesensor at atmospheric pressure. The next plot shows AFFF interferantadded. This results only in a slight shift to the left (more negativecompensation voltage) of the RIP peak. The CWA simulant DMMP is thenintroduced alone into the spectrometer and the typical monomer anddimmer peaks appear together with a corresponding reduction in the RIPpeak intensity. When 1% AFFF is added, the DMMP peaks are not effectedand only a slight leftward shift of the RIP is observed. The sameexperiment was repeated with DIMP and the effect of AFFF was negligible.Introducing MS and monitoring the negative ion peaks gave the similardata illustrating the lack of interference with AFFF. The conclusion isthat 1% AFFF has virtually no effect on the DMS practices of theinvention for CWA simulant spectra. Similar results were obtained withlive agents as well. This is an important breakthrough for CWAmonitoring.

The present invention enables method and apparatus for high fieldasymmetric waveform ion mobility spectrometry, which can be favorablyaugmented with other collection and separation techniques, and packagedin a compact system. Other than planar configurations are possible. DMSconfigurations which may be practiced according to the invention mayinclude method and apparatus using co-axial, cylindrical, flat, planar,radial, curved and other DMS electrode configurations. Embodiments ofthe invention may even be practiced augmented with prior art IMS and DMSfiltering.

The high sensitivity, rugged design and ease of use and setup ofembodiments of the invention are advantageous for many applications thatinvolve chemical detection. A simplified hand-held device of theinvention is dedicated to detection of a limited set of data and yetreliably detects and identifies ion species of interest. This practicemay be augmented by dual mode detections. The result is addedreliability in chemical detection in a simplified device.

It will now be appreciated that in practice of the invention we controlthe filter field, its electrical properties and its environment, in anion-mobility-based system, to amplify differences in ion mobilitybehavior for species separation. Species are then detected andidentified based on this function. We can further optimize the processby controlling ionization (such as by selection of sources of lower orhigher levels of ionization energy).

It should be appreciated that numerous changes may be made to thedisclosed embodiments without departing from the scope of the presentinvention. While the foregoing examples refer to specific embodiments,this is intended to be by way of example and illustration only, and notby way of limitation. It should be appreciated by a person skilled inthe art that other chemicals and molecules may be similarly ionized anddetected.

Therefore, while this invention has been particularly shown anddescribed with references to the above embodiments, it will beunderstood by those skilled in the art that various changes in form anddetails may be made therein without departing from the scope of theinvention encompassed by the appended claims.

1. A method for detecting infectious agents comprising: ionizing aportion of an airborne sample into ions, and filtering a portion of theions for at least one marker associated with an infectious agent withinthe sample using an ion mobility based filter to identify ionsassociated with the at least one marker.
 2. The method of claim 1,wherein the filtering includes flowing the sample through an asymmetricfield.
 3. The method of claim 2 comprising applying a compensation fieldto the asymmetric field to selectively pass ions through the asymmetricfield.
 4. The method of claim 3 comprising controlling at least onecondition of filtering.
 5. The method of claim 4 comprising storinginformation about conditions of filtering of at least one known markerand adjusting the conditions of filtering to enable the at least oneknown marker to pass through the asymmetric field.
 6. The method ofclaim 4 comprising storing information about conditions of filtering ofa plurality of known markers and scanning at least one condition offiltering to enable the plurality of lcnown markers to pass through theasymmetric field.
 7. The method of claim 1 comprising eluting a portionof the sample from a gas chromatograph before one of ionizing andfiltering the ions.
 8. The method of claim 1 comprising pre-filteringthe sample using a membrane.
 9. The method of claim 8, wherein themembrane includes at least one polymer.
 10. The method of claim 9,wherein the polymer includes one of Teflon® and dimethyl silicone. 11.The method of claim 1 comprising pre-filtering the sample to removeunwanted components.
 12. The method of claim 1, wherein the markerincludes at least one microorganism.
 13. The method of claim 1, whereinthe infectious agent includes at least one of protozoa, fungus,bacteria, and a virus.
 14. An ion mobility based infectious agentdetection system comprising: a sample introduction section forcollecting an airborne sample, the sample possibly including at leastone infectious agent marker, an ion source for ionizing a portion of thesample, an ion mobility based filter for filtering out the at least oneinfbctious agent marker, and a detector for detecting the at least oneinfectious agent marker.
 15. The system of claim 14, wherein the passingthrough includes flowing the sample through an asymmetric field.
 16. Thesystem of claim 15, wherein the filter is configured to apply acompensation field to the asymmetric field to selectively pass ionsthrough the filter.
 17. The system of claim 16 comprising an electroniccontroller for controlling at least one condition of the filter.
 18. Thesystem of claim 17, wherein the controller is configured for storinginformation about filter conditions associated with filtering at leastone known marker and adjusting the filter conditions to enable the atleast one known marker to pass through the asymmetric field.
 19. Thesystem of claim 17, wherein the controller is configured for storinginformation about filter conditions associated with filtering aplurality of known markers and scanning the filter conditions to enablethe plurality of known markers to pass through the asymmetric field. 20.The system of claim 14 comprising a gas chromatograph from which aportion of the sample is eluted before one of ionizing and pass throughthe ions.
 21. The system of claim 14 comprising a pre-filter forfiltering the sample using a membrane.
 22. The system of claim 21,wherein the membrane includes at least one polymer.
 23. The system ofclaim 22, wherein the polymer includes one of Teflon® and dimethylsilicone.
 24. The system of claim 14 comprising a pro-filter forremoving unwanted components.
 25. The system of claim 14, wherein themarker includes a microorganism.
 26. The system of claim 14, wherein theinfectious agent includes at least one of protozoa, fungus, bacteria,and a virus.